This phrase has often been interpreted as a rebuke of all doubt. The understanding is that Jesus is telling Peter that it was wrong to doubt, the inference being that all doubt is wrong. When this passage is preached in this way, the implication is that we should have complete control over our thought process and that all doubt can and should be removed from our minds. I have heard some preachers say that all doubt is sin.
Scripture does not support this assertion. I wonder if the preachers who make these claims have ever read the Psalms. David and the other psalmists ask lots of hard questions and reveal their doubts about God and frustrations with God. They are brutally honest about their struggles.
I also point to Jesus response to Thomas’ doubt. Jesus did not rebuke Thomas for his doubt; rather than a rebuke, Jesus offered evidence to Thomas (John 20:27). Jesus offered his battle scars to Thomas as proof of his identity.
If Jesus’ words to Peter are not a rebuke of all doubt, then what is the point of the question?
Perhaps we should understand the functional word to be “why.” Understood this way, Jesus is asking “what is at the core of doubt?” What is behind your doubt?
In defense of Peter, the fact that prior to that moment, no-one had ever walked on water would have been significant. The physical properties of water and the human body support the doubt. On the other hand, at this point in Jesus’ ministry, Peter had been exposed to previous suspensions of the laws of nature to know that Jesus was not limited by them.
Why did Peter doubt? The most obvious answer to this is that Peter focused on the seeming impossibility rather than upon the command of Jesus to come to him.
The efficacy of faith is determined by the reliability of the object of faith. Would it be unreasonable to supply the word “me” in Jesus’ question to Peter? Could the meaning of that question be properly interpreted as “why did you doubt me given the fact that you had seen me do so many incredible things before and I asked you to do this?”
In some cases doubt is driven by a desire for more evidence (as in the case of Thomas). The proper response to this form of doubt is to do additional investigation. But there is a point in our investigation of the facts about Jesus where we have to make a choice. The why question gets behind the evidence to expose what is at the core of how we interpret the evidence. We have to act on the evidence that is available, even as we continue our search for truth.
The why question that Jesus poses does not allow us to be content to remain in doubt. Agnosticism may be a legitimate layover point, but it is not a legitimate destination. As Geddy Lee points out, “If you choose not to decide, you still have made a choice.”
“Why” is the functional question.