See, Hear...and Touch It is true that the conclusion of the matter is what Jesus said: Blessed are they that have not seen and yet have believed. (John 20:29) But this is a contracted summary of the events.
Recall that Jesus himself connected Thomas's believing with touching:
Jesus said to Thomas, "Bring your finger here, and see my hands, and bring your hand here and put into my side; and do not be unbelieving, but believing!" (John 20:27)
All of Thomas's actions contributed to his believing, according to the narrative written by John. And notice that it took more than just seeing for the other ten disciples to believe, as well:
Being startled and frightened, they were thinking that they were seeing a spirit. And He said to them, "Why are you troubled, and why do doubts arise in your hearts? See my hands and my feet, that it is myself; touch me and see, for a spirit does not have flesh and bones as you see that I have." (Luke 24:37-39)
And while they were not believing because of their joy and were still marveling, He said to them, "Have you anything here to eat?" They gave Him a piece of broiled fish, and He took it and ate it before them. (Luke 24:41-43; see also 2 Peter 1:16-19)
And to further show that it more than just a distant (or close proximity "seeing") visionary response that was the basis of theirs (and Thomas's) eventual believing, notice the comments of John in his epistle:
What was from the beginning, what we have heard, what we have seen with our eyes, what we beheld and touched with our hands, concerning the 'Word of Life'...what we have seen and heard we proclaim to you also, so that you may have fellowship with...the Father, and with His Son Jesus Christ. (1 John 1:1-3)
Empirical Proof As apologists have pointed out, this was a crucial set of circumstances because it provided empirical proof of the Resurrection and Divinity of Christ...which is the linchpin of the Christian religion!
Modernity is fixated on scientific reasons for accepting any phenomenon: (1) testable (2) repeatable, and (3) observable by multiple witnesses. The post-resurrection scene fits all of these criteria: (1) all the disciples did hands-on testing, (2) it was repeated with a week in between (and with Jesus available for 40 days thereafter), and (3) not only Thomas, and the ten other Apostles, but hundreds of other people observed the resurrection (1 Corinthians 15:1-11).
Therefore, no one is with excuse for not believing in Jesus. The recorded testimony of eye-witnesses (similar to a scientific abstract in a peer reviewed journal?) is sufficient for any honest inquirer to see that Jesus is indeed Lord and God!
None of us in modernity have seen those events, but there is more than enough evidence upon which to base our Christian faith. And because of this we are blessed! (John 20:29)