Here is the “Doubting Thomas” story from Chapter 20 of the Gospel of John:

24 But Thomas, one of the twelve, called Didymus, was not with them when Jesus came.

25 So the other disciples were saying to him, “We have seen the Lord!” But he said to them, “Unless I see in His hands the imprint of the nails, and put my finger into the place of the nails, and put my hand into His side, I will not believe.”

26 After eight days His disciples were again inside, and Thomas with them. Jesus *came, the doors having been shut, and stood in their midst and said, “Peace be with you.”

27 Then He *said to Thomas, “Reach here with your finger, and see My hands; and reach here your hand and put it into My side; and do not be unbelieving, but believing.”

28 Thomas answered and said to Him, “My Lord and my God!”

29 Jesus *said to him, “Because you have seen Me, have you believed? Blessed are they who did not see, and yet believed.”

This story does NOT show that either the author of the Gospel of John or Jesus (as portrayed in this Gospel) understood “faith” to mean “belief that is based on no evidence”, nor does it show that the author of John or Jesus (as portrayed in this Gospel)  understood “faith” to mean “belief that is based on insufficient evidence”.  It does show that the author of John and Jesus (as portrayed in John) would clearly REJECT both of these definitions of “faith”.

1. Thomas “was not with them when Jesus came.” (verse 24)

Jesus had already shown himself in his resurrected body to the other disciples and had talked with them (20:19-23). If “faith” meant “believing on the basis of no evidence”, then Jesus had thereby made it IMPOSSIBLE for his other disciples to have “faith” in him. Since “faith” is a requirement for salvation, that means that Jesus had made it IMPOSSIBLE for any of the other disciples to be saved from eternal damnation. But this is absurd! Clearly, neither the author of this Gospel nor Jesus (as portrayed in this Gospel) think that “faith” means “believing on the basis of no evidence.”

Furthermore, according to the Gospel of John, Jesus’ inner circle of disciples had already been eyewitnesses to many amazing miracles, such as Jesus turning water into wine (2:1-11), walking on water (6:16-21), feeding thousands of people with a few loaves of bread (6:1-14), and raising Lazarus from the dead (11:38-48). So, in appearing to the disciples in his resurrected body, Jesus was not only presenting them with evidence of his resurrection and divinity, Jesus was providing them with OVERWHELMING evidence of his resurrection and divinity (by the combination of the previous amazing miracles plus his appearances to them in his resurrected body).

Thus, if “faith” was understdood to mean “believing on the basis of insufficient evience”, then Jesus was making it IMPOSSIBLE for his disciples to have faith in him, by presenting them with OVERWHELMING evidence of his resurrection and divinity. Since faith is a requirment for salvation, Jesus would have made it IMPOSSIBLE for his disciples to be saved from eternal damnation, if this is how Jesus understood the word “faith”. But this is absurd. Therefore, it is clearly the case that neither the author of the Gospel of John nor Jesus (as portrayed in that Gospel) took the word “faith” to mean “believing on the basis of insufficient evidence”.

2. “Unless I see in His hands the imprint of the nail…” (verse 25)

Thomas has previously seen Jesus perform a number of amazing miracles. Now the other disciples of Jesus tell him that they have seen and talked with the risen Jesus, yet Thomas remains unconvinced. He demands direct first-hand evidence, to see and even touch the risen Jesus for himself.

3. “Reach here your finger…” (verse 27)

When Jesus appears a second time to his gathered disciples, this time with Thomas present, he does not scold Thomas for demaning first-hand evidence; rather Jesus immediately offers the exact direct evidence that Thomas had required. So, now not only does Thomas have evidence for the resurrection and divinity of Jesus, but in view of the previous amazing miracles that Jesus performed and that Thomas witnessed, in view of the testimony of Thomas’ fellow disciples to the resurrection, and in view of the visible presence of the resurrected Jesus who is speaking directly to him, Thomas is also given OVERWHELMING evidence of the resurrection and divinity of Jesus (according to the Gospel of John).

So, if “faith” means “believing on the basis of no evidence” or “believing on the basis of insufficient evidence”, then Jesus has made it IMPOSSIBLE for Thomas to have faith in him. Since faith is a requirement for salvation, Jesus has made it IMPOSSIBLE for Thomas to be saved from eternal damnation. But this is absurd. So, clearly neither the author of the Gospel of John nor Jesus (as portrayed in that Gospel) understood “faith” to mean “believing on the basis of no evidence” or “believing on the basis of insufficient evidence”.

Jesus provides Thomas and his other disciples with OVERWHELMING evidence of his resurrection and divinity precisely in order to get them to “believe”, to have faith in him, to firmly believe that Jesus is the Son of God, sent by God to be the savior of humankind. Jesus sees no conflict between faith and strong evidence: “…do not be unbelieving, but believing.” (verse 27)

4. “Blessed are they who did not see, and yet believed.” (verse 29)

It has been clearly established that Jesus does NOT understand “faith” to mean “believing on the basis of no evidence” and that Jesus does NOT understand “faith” to mean “believing on the basis of insufficient evidence”. It is clear that Jesus (as portrayed in the Gospel of John) views faith as being compatible with having OVERWHELMING evidence in support of the belief in question. But verse 29 appears to suggest that “faith” might also be compatible with belief that is based on insufficient evidence.

But having something less than OVERWHELMING evidence for a belief is not the same thing as having insufficient evidence for that belief. Obviously, Christians who have not personally witnessed miracles being performed by Jesus and who have not personally seen and talked with the risen Jesus will not have the same high level and degree of evidence for their belief in Jesus as resurrected Son of God as the original disciples of Jesus. Christians who lived in the second century and following centuries do not (at least in general) have the OVERWHELMING evidence for this belief that the original disciples had (or are reported to have had by the Gospels). But this does not mean that the evidence such Christians have is insufficient evidence.

At least, it is not obvious that OVERWHELMING evidence is the only sort of evidence that will be sufficient to justify their belief. If a skeptic wishes to argue that only OVERWHELMING evidence will be sufficient evidence in the case of the belief that Jesus rose from the dead, that is fine by me, but a clear and strong argument is required for this view, because it is not obvious or self-evident that anything less than such powerful evidence must constitute insufficient evidence.

Because it is NOT obvious or self-evident that only OVERWHELMING evidence will be sufficient evidence for the resurrection and divinity of Jesus, we cannot reasonably assume that the author of the Gospel of John believed that only such evidence would be sufficient evidence. We must allow for the very real possibility that the author of this Gospel and Jesus (as portrayed in this Gospel) thought that the faith of later generations of Christians could be based on sufficient evidence which was, however, something less than OVERWHELMING evidence.

The author of the Gospel of John may reasonably be presumed to have viewed the “testimony” presented in this Gospel to provide sufficient evidence (but not overwhelming evidence) for the resurrection and divinity of Jesus, as indicated by the verses that immediately follow the “Doubting Thomas” story:

30 Many other signs therefore Jesus also performed in the presence of his disciples, which are not written in this book;

31 but these have been written that you may believe that Jesus is the Christ, the Son of God; and that believing you may have life in his name.

Although the author of John and Jesus (as portrayed in that Gospel) appear to think that “faith” is compatible with both having OVERWHELMING evidence for a belief and also with having something less than OVERWHELMING evidence for the belief, it is not at all clear that “faith” is viewed as being compatible with belief on the basis of insufficient evidence.

In any case, it is clear that neither the author of John nor Jesus (as portrayed in that Gospel) undstand “faith” to mean “belief on the basis of insufficient evidence”. Therefore, the claim that sincere and devout Christian believers (who regularly read and study the Gospels) think that “faith” means “belief on the basis of insufficient evidence” is highly questionable. (Perhaps there are many Christians who are not sincere or not devout and who don’t bother to carefully read and study the Gospels, and such Christians might well have an understanding of “faith” that is different than what Jesus had or than what the author of the Gospel of John had.)