St. Thomas the Apostle is remembered primarily for two things: that he was the one who did not believe in the Resurrection, and that he brought Christianity to India. Doubting Thomas is a bit of an unfair reputation. So far as we know, none of the Apostles believed before seeing Jesus except St. John who saw the empty tomb and believed. It is simply that his doubts are recorded in such a powerful fashion as we read today. He immediately believed. He experienced many hardships and went to a faraway land to preach the Gospel. There he was killed for the faith.
He was not a lifelong doubter once he saw the evidence with his own eyes, but it cannot be said simply that Thomas believed because he saw. Many people might have seen the same thing and still doubted. St. Thomas received his faith not by investigation. St. Thomas received his faith from the Father.
Faith is not a human accomplishment. Faith is a gift. Faith is not gritting our teeth and insisting that we will believe. Faith is a gift. Faith is not something we should be proud of as if we were better people than those who do not believe. Faith is something we ought to be grateful for because it is a gift. Faith is something that we ought to ask God for every day. And if we begin to doubt, there are two mistakes we can make: trying to fight the doubts on our own or accepting the doubts as wisdom. If we begin to doubt, we must turn to God and ask for more faith.
We receive knowledge from our parents and the Church. We know about Christianity because of them and the books we read. But faith is something different. If the whole world abandoned Christianity, and it was just you alone with no support, if they all told you that it was pretend, that it was just another story like Santa Claus or the Easter Bunny, is there something within you that would still believe? Is there something within you right now that believes in God without consideration of any argument or reason? That is faith. It does not seem strong because if we test it ourselves, it will fall apart quickly. The test of our faith comes from the outside: persecution, suffering, martyrdom. That is when we find out how strong faith really is.