D.A. Carson spoke in church this past Sunday on ME! ...well my name anyway. I'm going to give you a brief of the sermon, because it was really good!
The point of the sermon was not doubt, this passage John 20:24-31 is many times mistakenly used to assuage people's doubts. The Bible's answers for doubts are dependant on the cause.
The cause of Thomas' doubt was that he was a skeptic.
1. Cry of the Disappointed Skeptic - vs. 25
Everything else that we know about Thomas from the Bible shows that he was a devout 1st Century Jew that believed that the Old Testament was the word of God. He was just disappointed by the fact that he believed that Christ was dead. He was struggling because he didn't want to confuse FAITH with GUILIBILITY. For example: He felt like he had fallen for a "faith healer" shyster and didn't want to fall for that again. He didn't want to be known as one that would believe anything.
2. Adoration of an Astonished Skeptic - vs. 26-28
"My Lord, and my God!" What an answer! He didn't say: "Oops, you ARE alive" or "Bummer, I made a mistake." Instead he gave a confession of Christ's Deity. Why did Thomas do this? If you think about it, he did have a week between the time that the Disciples told him of Christ's Resurrection and when he finally saw Him. He had a week to think that maybe the other Disciples were right, maybe Christ WAS alive. A week to mull over all he had seen Jesus Christ do and teach. And when he finally saw Jesus Christ in the flesh... "My Lord, and my God!" came forth. His faith was sealed!
3. Example and Role of a Converted Skeptic - vs. 29-31
Faith is what it comes down to. Not to be confused with today's definition of a private belief not connected to truth. Our Faith is connected to something tangible, it is based on evidence. Vs. 29 can sometimes be taken as: "Those that believe without seeing are MORE blessed that those that have to see." All are blessed who believe. We are the ones that have to believe without seeing. We won't be able to put our hands in His side or feel the nail prints. Our faith has to be based on the truth told to us by the witnesses to the truth.
Nutshell: The Bible doesn't ask us to believe an untruth. And in believing, we will have life!