Appendix: The Rationality of Faith

Alex Rosenberg, professor of philosophy at Duke University and author of the book The Atheist’s Guide to Reality, once debated Christian philosopher William Lane Craig on the question whether faith in God is reasonable. Rosenberg began his argument with the claim that faith could never be reasonable because “by definition, faith is belief in the absence of evidence.”Quoted in Daniel Howard-Snyder (2016), “Does Faith Entail Belief?” Faith and Philosophy 33 (2):142-162. A video of the debate is available here. Rosenberg is not alone in this opinion. Many people think that having faith means believing something without evidence or believing with greater confidence than the evidence justifies. Harvard cognitive psychologist Steven Pinker writes that faith is “believing something without good reasons to do so.”Steven Pinker, “Less Faith, More Reason,” The Harvard Crimson (2006). Similarly, evolutionary biologist Richard Dawkins defines faith as “belief in spite of, even perhaps because of, the lack of evidence.”Quoted in Daniel Howard-Snyder (2016), “Does Faith Entail Belief?” Faith and Philosophy 33 (2):142-162. This conception (or misconception) of faith is so prevalent that even Merriam-Webster’s 11th Collegiate Dictionary includes the following among its definitions of the word ‘faith’: “firm belief in something for which there is no proof.”Merriam-Webster’s 11th Collegiate Dictionary, “faith,” definition 2b(1). But is that what biblical faith—the kind of faith described in scripture—amounts to?

People can use the same word to mean different things. When some people use the word ‘faith,’ apparently, they mean belief in something for which there is little evidence. That kind of faith is sometimes called blind faith. If people want to use the word ‘faith’ to mean blind faith, that’s fine with me. They’re welcome to use the word however they like. But that doesn’t change what I mean when I use the word ‘faith,’ and it definitely doesn’t change what the Bible means. I will argue that biblical faith is not blind faith. It’s not “firm belief in something for which there is no proof.” Biblical faith is rooted in evidence about God’s existence, goodness, and trustworthiness.

Not once does the Bible tell us to ignore evidence or to believe on insufficient evidence. Quite the contrary. Consider Jesus’ words to his disciples: “Believe me when I say that I am in the Father and the Father is in me; or at least believe on the evidence of the works themselves.” (John 14:11, NIV) Clearly Jesus is not instructing his disciples to believe his words without evidence, nor to trust him with greater confidence than the evidence justifies. To the contrary, he encourages them to cultivate their faith in him by considering the evidence about his identity. What is that evidence? His “works”—the things he is doing, and especially the miracles he is performing—give his disciples ample reason to believe that he is who he claims to be and that his words are not spoken merely on human authority. Think about it: They’ve seen him heal the sick, restore sight to the blind, make the lame walk, and even raise the dead to life. They’ve seen him walk on water! They heard him command the wind and waves to be still, and the storm obeyed him!

Likewise, I contend, our faith in God should be based on the good evidence we have about His faithfulness, His goodness, His power, and His trustworthiness. However, several passages of scripture—taken out of context—may seem to support the opposite view. In Hebrews 11:1-2, we read: “Now faith is confidence in what we hope for and assurance about what we do not see. This is what the ancients were commended for.” (NIV) Similarly, the apostle Paul says “we walk by faith, not by sight” (2nd Corinthians 5:7, NASB). In John 20:29, Jesus himself says “blessed are those who have not seen and yet have believed” (NIV). At first glance, these statements seem to imply that biblical faith isn’t based on evidence, and that it is commendable to have faith when there is little evidence to support it. Is that really what these verses mean? Let’s meditate on each of these verses, paying attention to their contexts.

We’ll begin with Hebrews 11:1. This verse sometimes is thought to provide a definition of faith. Let’s look at several popular translations:

“Now faith is confidence in what we hope for and assurance about what we do not see.” (NIV)
“Now faith is the assurance of things hoped for, the conviction of things not seen.” (NASB)
“Now faith is the substance of things hoped for, the evidence of things not seen.” (KJV)

Taken out of context, this verse sounds as though it is offering a general definition of faith, a definition which sounds a lot like “blind” faith (especially in the NIV translation). When we examine the context, however, it is clear that the writer of Hebrews isn’t trying to define the concept of faith in general. He is talking specifically about our faith in God’s promises for our future, and he certainly isn’t suggesting that our faith is blind:

Remember those earlier days after you had received the light, when you endured in a great conflict full of suffering. Sometimes you were publicly exposed to insult and persecution; at other times you stood side by side with those who were so treated. You suffered along with those in prison and joyfully accepted the confiscation of your property, because you knew that you yourselves had better and lasting possessions. So do not throw away your confidence; it will be richly rewarded. You need to persevere so that when you have done the will of God, you will receive what he has promised. For, “In just a little while, he who is coming will come and will not delay.” And, “But my righteous one will live by faith. And I take no pleasure in the one who shrinks back.” But we do not belong to those who shrink back and are destroyed, but to those who have faith and are saved. Now faith is confidence in what we hope for and assurance about what we do not see. (Hebrews 10:32 - 11:1, NIV)

In context, Hebrews 11:1 is clearly referring to God’s promise to reward those who persevere through trials. The things we “hope for” but “do not see” are the rewards for our faith. This verse isn’t suggesting that we see no evidence of God’s trustworthiness. To the contrary, we do see plenty of evidence that God keeps his promises. Our faith in God’s promises is rational because—as the writer of Hebrews points out earlier in that same passage—we know God (verse 30), and we know that “he who promised is faithful” (verse 23). We have “knowledge of the truth” (verse 26), and that evidence-based knowledge is the foundation of our faith, not blind speculation or wishful thinking.

Next, let’s consider Paul’s comment that “we walk by faith, not by sight” (2nd Cor. 5:7). Out of context, the contrast between “faith” and “sight” might seem to imply that faith is blind. However, when we examine the preceding verses, it is immediately clear that Paul is not encouraging blind faith. He is not contrasting faith and evidence; rather, the contrast has to do with the things that motivate us. Just a few verses earlier, he writes:

We are afflicted in every way, but not crushed; perplexed, but not despairing; persecuted, but not forsaken; struck down, but not destroyed… But having the same spirit of faith, according to what is written, “I believed, therefore I spoke,” we also believe, therefore we also speak, knowing that He who raised the Lord Jesus will raise us also with Jesus… For momentary, light affliction is producing for us an eternal weight of glory far beyond all comparison, while we look not at the things which are seen, but at the things which are not seen; for the things which are seen are temporal, but the things which are not seen are eternal. (2nd Corinthians 4:8-18, NASB)

In this context, the contrast between faith and sight obviously has nothing to do with the evidence upon which our faith is based. Rather, Paul is contrasting two kinds of motives that may guide our lives. We may be motivated by temporary, earthly rewards—the things we can see—or we may be motivated instead by our faith in God’s promise of “an eternal weight of glory far beyond all comparison.” We cannot yet see the latter reward, but we have faith in God’s promise because we know “that He who raised the Lord Jesus will raise us also.” Our faith comes from our knowledge of Christ’s resurrection. Because of this evidence-based knowledge, we have faith to pursue unseen, eternal things instead of fixing our eyes on the visible but temporary treasures of this world. That is what it means to “walk by faith, not by sight.”

The third scripture passage that may appear to contradict my thesis is the famous story of “doubting Thomas,” found in the gospel of John. Thomas, one of Jesus’ twelve disciples, refused to believe that Jesus had risen from the dead: “Unless I see the nail marks in his hands and put my finger where the nails were, and put my hand into his side, I will not believe.” (John 20:25, NIV) Jesus later presents Thomas with that very opportunity, and says to him: “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.” (verse 29)

Taken out of context, this statement may seem to imply that faith is more virtuous or commendable when it isn’t based on evidence. But is that really the point Jesus is making? Is he really scolding Thomas for being rational, for being careful not to believe something on insufficient evidence? As the rest of John’s gospel makes clear, that is not what is happening here. Thomas’s doubts were irrational, not rational. Even before he saw the resurrected Christ with his own eyes, Thomas had plenty of evidence that Jesus had risen, but he irrationally refused to acknowledge that evidence.

What evidence did Thomas have? Well, for starters, many of his closest friends had already told him that they had seen Jesus alive again. Mary Magdalene told him about her encounter with Jesus outside the tomb (verse 18). Likewise, other disciples recounted how Jesus had visited them and showed them his pierced hands and side (verses 20-25). It was their eyewitness testimony that prompted Thomas’s cynical remark in the first place! Furthermore, Thomas himself had witnessed many miracles—including several resurrections—that Jesus had performed before his death. Thomas knew that God had power to raise the dead. He had seen it happen before his very eyes!

Yet, despite all of this evidence, Thomas refused to believe. He refused to trust even his closest friends, writing them off as either liars or lunatics when they told him what they had witnessed. Worse than that, he refused to trust Jesus himself. Jesus had warned his disciples that he would be killed and rise again after three days (Mark 8:31-32). Thomas had good reasons to believe that Jesus’ words were true, yet he doubted. His doubts were not rational.

So, Jesus isn’t scolding Thomas for being rational. He’s not scolding Thomas at all. His words are incisive, but gentle: “Put your finger here; see my hands. Reach out your hand and put it into my side. Stop doubting and believe.” (John 20:27) Jesus responds to Thomas’s doubts by providing still more evidence!

It is also worth noting why the apostle John recorded this incident in his gospel. John explains his motive in the very next verse. Immediately after the story of doubting Thomas, he writes: “Jesus performed many other signs in the presence of his disciples, which are not recorded in this book. But these are written that you may believe that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name.” (verse 30)

So, John recorded this testimony for the sake of people like you and me, who find ourselves in circumstances similar to Thomas’s situation. Although we don’t presently see Jesus with our own eyes, we are confronted with evidence of his power over death. We should acknowledge the testimonial evidence from trustworthy eyewitnesses, just as Thomas should have done. John is doing for us what Jesus did for Thomas: encouraging us to consider the evidence we have, and providing us with still more. Far from encouraging “blind” faith, the story of doubting Thomas actually teaches the very opposite. Our faith is based on evidence, including testimonial evidence, and our doubts arise from ignoring that evidence.

It is clear from these examples that the kind of faith the Bible teaches is not “blind” faith, but faith based on good evidence, evidence of God’s faithfulness and trustworthiness. But that still doesn’t answer our central question: What does it mean to have faith? What is faith, exactly? Earlier, I argued that Merriam-Webster’s definition isn’t an accurate depiction of the biblical kind of faith, so let’s try another dictionary. The Oxford English Dictionary is widely regarded as the most authoritative dictionary of the English language. It provides a definition that—in my opinion—accords much better with the biblical concept of faith. According to the OED, faith is “confidence, reliance, trust (in the ability, goodness, etc., of a person; in the efficacy or worth of a thing; or in the truth of a statement or doctrine).” That is how I understand the biblical notion of faith. To have faith in God is to have confidence in his ability and goodness, to rely on him, and to trust him. To have faith in Jesus’ name is to have confidence, reliance, and trust in its efficacy and worth. To have faith in his words is to trust and rely on them, and to have confidence that they are true.

Of course, the Bible wasn’t written in English, so looking up the English word ‘faith’ in a dictionary isn’t going to settle the question of what the Bible means when it uses that word. Most of the New Testament originally was written in Greek. The Greek word for faith is πίστις, transliterated pistis. (Transliteration is when you take a word from another language and spell it using letters from your own language.) I don’t speak Greek, but I looked up this word in a couple of Greek dictionaries (Greek lexicons), and its meaning (or range of meanings) is similar to the English word ‘faith’ as defined by the Oxford English Dictionary: it involves confidence, reliance, and trust.

The Greek word pistis is a noun, like the English word ‘faith.’ Unlike English, however, the Greek language also has a corresponding verb, pisteuo, which means to have faith. Since English doesn’t have a verb form of the word faith, Bible translators usually translate the Greek verb pisteuo into English as the word ‘believe.’ Almost all occurrences of the word ‘believe’ in the New Testament are translations of the Greek word pisteuo. For example:

“For God so loved the world, that He gave His only begotten Son, that whoever believes [pisteuo] in Him shall not perish, but have eternal life.” (John 3:16)
“… The word is near you, in your mouth and in your heart—that is, the word of faith [pistis] which we are preaching, that if you confess with your mouth Jesus as Lord, and believe [pisteuo] in your heart that God raised Him from the dead, you will be saved; for with the heart a person believes [pisteuo], resulting in righteousness, and with the mouth he confesses, resulting in salvation.” (Romans 10:8-10)

In these verses, the word translated into English as “believe” is the Greek word pisteuo—the verb form of the word pistis (faith).

Now, we’ve already seen that dictionaries don’t always agree with each other about the meaning of a word. For example, Merriam-Webster’s Dictionary and the Oxford English Dictionary gave significantly different definitions for the English word ‘faith.’ The same thing is true of Greek dictionaries: they don’t all give the same definitions for the words pistis and pisteuo. So, how can we figure out exactly what these words mean when they are used in scripture?

The best way to determine the meaning of a word is not just to look it up in a dictionary, but also to study how the word is used. That’s how lexicographers (people who make dictionaries) figure out the meanings of words in the first place: they study how the words are actually used. Likewise, when we’re trying to understand what the word ‘faith’ means in the Bible, we should study how the word is used in scripture. Thankfully, we have a lot of scriptural evidence to go on. The noun pistis (faith) and the corresponding verb pisteuo (to believe, or to have faith) are used hundreds of times in the New Testament.

In fact, there’s an important clue about the meaning of pisteuo in the above passage from Romans 10. I still remember the moment when I first noticed it. I was a grad student at Princeton, and I was just outside the philosophy department building, waiting for the shuttle bus to take me back to my apartment. To pass the time, I was reading the Bible on my phone, and I came to this passage from Romans 10. I distinctly remember, as I was reading, this question that hit me all of a sudden: “Wait a minute… why does Paul say that I should believe in my heart, and that it is with the heart a person believes? Don’t we believe with our minds rather than our hearts?”

When the Bible talks about our hearts, it’s not referring to our blood-pumping organs, obviously. It’s referring to the seat of our desires and values—the things we love and care about, the things that motivate our actions. I had just taken some graduate seminars in ethics and in the philosophy of personal identity, and I had been thinking a lot about the relationship between the heart and the mind. So, as I was pondering this at the bus stop, and wondering why Paul says we should believe in our hearts, I suddenly realized what he was saying. I realized that believing in our hearts, or having faith, is not just a matter of holding true opinions in our minds—for example, believing it’s true that God exists and it’s true that Jesus rose from the dead. James 2:19 says that even the demons believe those things, and they shudder!

The kind of faith Jesus commands us to have, and the kind of faith Paul reminds us we need, goes much deeper than mere intellectual assent to the truth of certain claims. As I now understand, a decision to place our faith in Christ is not just a matter of changing our minds—deciding to believe something that we previously thought was false. Placing our faith in Christ primarily involves a change in our hearts—a change in our deepest desires and motives, a change in what we value and care about.

Around that same time in my life, something else also happened that got me thinking more carefully about the concept of faith. While I was studying at Princeton, I became friends with several other grad students in the philosophy department who were also Christians. One of these friends was Lara Buchak, who is now back at Princeton as a tenured professor of philosophy. While we were grad students, she wrote a paper titled “Can it be Rational to Have Faith?” which was later published (twice, actually)Lara Buchak, “Can it be rational to have faith?”, in Jake Chandler and Victoria S. Harrison (eds.), Probability in the Philosophy of Religion (Oxford, 2012), 225-247; reprinted in Louis P. Pojman and Michael Rea (eds.), Philosophy of Religion: An Anthology, 7th edition (Wadsworth, 2014). and has generated a lot of discussion about faith in the philosophical community. That paper inspired me to think more carefully about the nature of faith and what it means to have faith.

Dr. Buchak’s arguments defending the rationality of faith are complex and technical, but she also offers some simple, easy-to-understand insights about the nature of faith. In a video published by The Center for the Philosophy of Religion at the University of Notre Dame, Buchak summarizes her understanding of faith this way:

There’s a naïve idea out there that faith is something like believing more strongly than the evidence suggests, or even believing without any evidence at all. But when we think about ordinary cases of faith, like faith in a friend, or faith in your spouse, this isn’t really what’s going on. You don’t have faith in a friend by believing something about the friend that you don’t have any evidence for. In fact, usually when you have faith in your friend, or faith in your spouse, you do so precisely because you have a lot of evidence that they’re a trustworthy person.

So, what is faith, exactly? What do these cases of faith have in common? Well, what I propose is that to have faith in some claim is to be willing to take a risk on that claim without looking for more evidence. So, for example, to have faith that your friend will pick you up at the airport is to be willing to take a risk on the claim that that’s true. For example, you’re not going to have some backup transportation in case she doesn’t show up. And you also have to be willing to take that risk without looking for more evidence. So, for example, you’re not going to call her every ten minutes just to double-check that she’s really on her way. That’s a really ordinary example of faith.

So, in general, faith doesn’t require believing more strongly than the evidence suggests. What faith requires is being willing to act on the relevant claim without looking for more evidence—to be willing to act on the basis of the evidence you already have.“Can faith be rational? (Lara Buchak),”
Copyright: Center for Philosophy of Religion. Permission to embed this video is granted by the copyright holder via YouTube’s Terms of Service.This video was uploaded to YouTube by the copyright holder, who enabled the option to embed the video in the YouTube “Embeddable Player.” According to the Terms of Service, section 6C, this constitutes an agreement to “grant each user of the Service a non-exclusive license to access your Content through the Service, and to use, reproduce, distribute, display and perform such Content as permitted through the functionality of the Service and under these Terms of Service.”

According to Buchak’s definition, having faith in the truth of a claim means being “willing to take a risk on that claim without looking for more evidence.” Likewise, we might say, to have faith in a person is to be willing to act on your belief that they are trustworthy, without looking for more evidence first. So, faith involves more than just a belief. Faith is a willingness to act, and a readiness to act, on what we believe.

You may have heard the story of Charles Blondin,His real name was Jean François Gravelet, but he adopted the stage name Charles Blondin for most of his performing career. the daredevil who walked across the Niagara Falls Gorge on a tightrope. He performed this feat many times—more than 300 times, in fact. (He never fell, and he was still performing in his 70s.) On one occasion, Blondin even carried his manager, Harry Colcord, across on his back.For more of the story, see this. Now, it’s one thing to believe that Blondin can carry a person across the gorge on a tightrope. But being ready and willing to take that ride is quite another matter! Many people believed Blondin could do it; but when Blondin asked for volunteers, not so many people raised their hands. Blondin’s manager, Harry Colcord, may have been the only person who actually had faith in Blondin’s abilities.

Once we understand this volitional aspect of faith, it’s easier to see why faith isn’t just a matter of what we believe in our minds; it has just as much to do with our hearts. The decision to have faith in God often—perhaps always—involves a change in our hearts (our values and motives) rather than in our beliefs. That is why Christians who already believe in the existence of God still have to choose, continually, to place their faith in Him.

To better understand how faith works, and how it relates to both our hearts and our minds, I find it helpful to employ an idealized model that philosophers sometimes use to represent how our beliefs and our values both play a role in the decisions we make. Bayesian decision theory is a mathematical model—that is, a mathematical representation—of how an ideally rational person makes decisions. (An ideally rational person is someone who reasons correctly, or the right way, in a certain sense to be explained below.) Bayesian decision theory is named after Reverend Thomas Bayes (1701-1761), a Christian minister and mathematician who developed some of the mathematical foundations on which the model is based.

Before introducing this model, let me clarify what is meant by rationality in this context. Philosophers distinguish two main types of rationality, or reasonableness:

  1. Epistemic rationality concerns what it’s reasonable to believe. A belief is epistemically rational for you when it’s a reasonable thing for you to believe, given your other beliefs and the evidence you have.
  2. Practical rationality (also called pragmatic rationality) concerns what it’s rational to do. A choice or action is practically rational for you when it’s a reasonable thing for you to do, given your beliefs, desires, and values.
For further discussion of rationality, see my other online ebook: Skillful Reasoning: An Introduction to Formal Logic and Other Tools for Careful Thought, especially the chapter on Evidence and Rationality.

I have already argued that biblical faith is rational in the first sense. Biblical faith is not “blind” faith but evidence-based faith. The beliefs involved in biblical faith are epistemically rational, insofar as they are based on the abundant evidence we have of God’s faithfulness and trustworthiness.For a careful and compelling discussion of the evidence for Christianity, I recommend the works of Oxford philosopher Richard Swinburne. His book The Existence of God (Oxford: Oxford University Press, 2004) is a good place to start. I also recommend New Testament professor Craig Keener’s book Miracles Today: The Supernatural Work of God in the Modern World (Grand Rapids: Baker Academic, 2021), which provides a thoughtful discussion of evidence from miracles, including some medically well-documented cases of sudden healing that cannot be attributed to mere psychosomatic effects or other natural causes. However, as I have emphasized, faith is more than mere belief: it is a willingness to act, and a readiness to act, on what we believe. Can acting on faith be rational in the practical sense? What is the right way to reason when making a choice about whether to act on faith?

According to Bayesian decision theory, whenever we face a decision where we have to choose between two or more possible actions, there are two factors that should play a role in determining which action we choose to perform:

  1. Our expectations (degrees of belief) about the likely outcomes of our actions—in other words, how likely or probable we think each possible outcome is.
  2. The degrees to which we value or disvalue the various possible outcomes—in other words, how much the outcomes are worth to us.

Bayesian decision theory says that the most reasonable (or rational) thing to do is to choose the action with the highest “expected utility.” The expected utility of an action depends on both our beliefs and our values. To calculate the expected utility of an action, we multiply the probability of each possible outcome times the degree to which we value that outcome, then add those numbers together.

For example, suppose a particular choice has two possible outcomes: one GOOD and one BAD. Then the expected utility of that choice is EU = (probability of GOOD outcome × positive value of GOOD outcome) + (probability of BAD outcome × negative value of BAD outcome)

Let’s apply this to the tightrope scenario. Imagine you’re Harry Colcord, Blondin’s manager. Blondin has just invited you to ride across the tightrope on his back, and you have to decide whether or not to accept the invitation. What factors influence your decision? First of all, your expectations about the likely outcomes are obviously relevant. You’ve seen Blondin perform this stunt many times, so let’s say you are 99% confident that he’ll be successful, winning fame and fortune for both of you if you let him carry you across.

Blondin carrying Colcord
Blondin carries Colcord across the Niagara Falls GorgeThis scene was captured by photographer William England in 1859. The image is in the public domain, since its copyright has expired.

On the other hand, you still have that nagging 1% doubt: you think there’s a 1% chance that if you accept the offer, you’ll both end up falling to your deaths. What should you do? Well, that depends on how much you value or disvalue the various possible outcomes of your choice. If you accept and he makes it across, that’s the best case scenario: you win fame and fortune. For concreteness, let’s assign that outcome a value of 100. (The units don’t matter; I’m just using this model for illustration.) If you accept and he falls, though, that’s really, really bad. Let’s assign that outcome a negative value of -10,000. Given your beliefs and values, the expected utility of accepting Blondin’s offer is:

(.99 × 100) + (.01 × -10000) = -1

On the other hand, if you refuse the offer, you’ll miss out on the opportunity for fame and fortune, but you still expect to live a moderately prosperous life as Blondin’s manager if he makes it across without you. Let’s assign that a value of 50. If he falls, you’ll lose your income but at least you’ll survive. Let’s assign that a value of -50. Given these values, the expected utility of refusing Blondin’s offer is:

(.99 × 50) + (.01 × -50) = 49

Should you accept Blondin’s offer? No way! The expected utility of accepting (-1) is lower than the expected utility of refusing (49).

In real life, obviously, we don’t make decisions by assigning numbers to our beliefs and values and then performing a mathematical calculation. Remember, this is just a model, a simplified representation of how decision-making really works. Real-life decisions are more complicated, but this simplified model helps to clarify how our beliefs and our values play separate but related roles in the decisions we make.

Now, consider this: In the example I just gave, you decided not to ride across the tightrope on Blondin’s back, and that choice was perfectly reasonable, given your beliefs and values. But could it ever be reasonable (rational) to make the opposite choice? What would have to change in order for you to decide to trust Blondin with your very life, and have faith that he will carry you across safely?

There are two distinct ways in which your motivational structure might change. On one hand, the strength of your beliefs might change: you might become even more confident in your belief that he can do it. If your confidence rose from 99% to 99.9%, for example, that would be enough to raise the expected utility of accepting the offer above the expected utility of refusing. (You can crunch the numbers, if you want, and confirm this result.) But there is another way in which your motives can change, even if you don’t get any new evidence and your beliefs don’t change at all. Your values can change.

For example, suppose as you begin to reflect on how much you care about your friendship with Blondin, you decide that trusting him is worth more to you than just the fame and fortune, because it will deepen the friendship between you. So instead of assigning a value of 100 to the “best case scenario” outcome, you raise the value of that outcome to 200. In that case, the expected utility of accepting Blondin’s offer would be higher than the expected utility of refusal. Your beliefs haven’t changed at all, but your values have changed. You’ve had a change of heart, not a change of mind.

Similarly, it is possible to make a deliberate decision to have faith in God—and to be fully rational in doing so—even without gaining any new evidence. Of course, having faith in God does require believing that God exists and that he is trustworthy. Those beliefs are rational insofar as they are based on good evidence, and we do have abundant evidence of God’s trustworthiness—including, for example, the testimonies of thousands of Christians throughout the history of the church and the testimonial evidence found in the Bible itself. However, as explained above, faith is more than mere belief: it is a readiness and willingness to act on what we believe. This volitional aspect of faith is also rational, when our desires and values are appropriately oriented to recognize God as the greatest and highest good.

Thus, biblical faith is both epistemically rational and practically rational. Faith in God is epistemically rational because it is—or at least it can be and should be—based on the good evidence we have of God’s trustworthiness. Biblical faith is not blind faith, but reasonable, rational, well-founded faith. Our faith also is practically rational, in the sense described by Bayesian decision theory. Acting on our faith in God is always the rational thing to do if we value and desire God above all else, as Jesus teaches us: “‘Love the Lord your God with all your heart and with all your soul and with all your mind.’ This is the first and greatest commandment.” (Matthew 22:37-38, NIV)

Growing faith

The biblical kind of faith is powerful. Jesus told his disciples, “if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.” (Matthew 17:20) Mustard seeds are tiny—in fact, they were the smallest cultivated seeds in the area where Jesus did his ministry—but they grow like crazy.Several different species of plant are called “mustard” today. The species to which Jesus was referring may have been either Sinapis nigra (a type of black mustard) or Salvadora persica, commonly known as the mustard tree. Both species have tiny seeds, about the size of a pinhead. Sinapis nigra can grow to a height of nearly ten feet, while Salvadora persica often exceeds twenty feet. In another passage of scripture, Jesus compares the Kingdom of God to a mustard seed, pointing out that “a mustard seed … is the smallest seed planted in the ground. But when you plant the seed, it grows. It becomes the largest of all garden plants.” (Mark 4:31-32, NIRV)

We can’t produce faith by our own efforts, since faith “is the gift of God,” as the apostle Paul writes in Ephesians 2:8. So, when we lack faith, we need to ask God for it. After we have received faith, though, we should nurture it.

With that analogy in mind, I’d like to offer a few suggestions for how we can nurture and grow our faith in God. There are several ways in which we can nurture the faith that God has given us, so that it grows like a mustard seed:

  1. First of all, once we recognize that biblical faith isn’t blind faith, it should be obvious that ignoring evidence is not a way to build faith in God. Instead, we should do exactly the opposite: rather than ignoring evidence, we should pay close attention to the evidence. We should meditate on the evidence of God’s faithfulness, remind ourselves of it, ponder it, ruminate on it. For example, I’ve found that my faith is strengthened whenever I reflect on testimonies I’ve heard about God’s faithfulness in other people’s lives, and my faith grows even more when I remember how He has been faithful in my own life—how He has answered prayers, often in unexpected ways, and how He has led me through times of difficulty and uncertainty, always working “all things together for good” (Romans 8:28) in ways I couldn’t have anticipated. In hindsight, I can see clearly that God has been carrying out his plans for me all along, even during seasons when I felt that He wasn’t. So, reflecting on His faithfulness in the past builds my faith to trust him with my future.
  2. Second, we should reconsider our values and priorities. That’s because faith isn’t just a matter of what we believe in our minds. As we have seen, it involves what we value or care about in our hearts. Are we seeking first His kingdom and His righteousness (Matthew 6:33) as Jesus taught us in his famous Sermon on the Mount? If not, we need to reorient our priorities toward Him.
  3. Third, our faith grows when we act on it. Faith is a gift from God, but we shouldn’t expect Him to give us more when we’re not using the faith he gave us already. However, when we do act on faith—even if we have only a mustard seed’s worth of faith to act on—God will prove himself faithful, and that will give us even more evidence of his faithfulness, growing our faith until it becomes the largest, tallest plant in the garden of our lives.