Doubt can be very helpful. It encourages us to discern. If we immediately accepted everything we heard or read, life could get very confusing. At the same time, doubt must have limits. When we can't stop being skeptical, then doubt becomes an obstacle that keeps us from recognizing and embracing the truth.
Today many people doubt the existence of God. It is difficult to accept what cannot be proven. However, even believing Christians have doubts: Does God truly love me? Is God really walking with me? Is my lifestyle truly what God is calling me to do?
Thomas is not afraid to admit his doubts. In response, Jesus does not rebuke or renounce him. Instead, Jesus comes to Thomas where he is and gently invites him to change from a position of unbelief to belief. Jesus shifts the focus from doubt to faith. The reply of Thomas is the clearest and most powerful confession of Jesus' identity in the Gospel of John: "My Lord and my God".
We may never know for certain whether or not St. Thomas later evangelized in far away places such as India. What we do know is that Jesus gave Thomas what he needed to put aside his doubts, what he needed to recognize Jesus as the true revelation of God, and what he needed to give the rest of his life witnessing to his Lord and his God.
Lord, change my unbelief into belief.