Thomas the Apostle, also called Didymus (meaning "Twin," as does "Thomas" in Aramaic") was one of the Twelve Apostles of Jesus. He was perhaps the only Apostle who went outside the Roman Empire to preach the Gospel. He is also believed to have crossed the largest area, which includes the Parthian Empire and India.
The text chosen for the Feast of St. Thomas from the Gospel is often mistakenly referred to as that of “Doubting Thomas”. However, that is a misnomer. Jesus does not use the word doubt in these verses. Rather, Jesus chides Thomas for being unbelieving. The story focuses on the grounds of faith. Thomas seeks tangible proof which the disciples are unable to provide. Jesus provides this for Thomas and in so doing asks him to move from unbelief to faith.
Thomas does not touch the hands and side of Jesus as Jesus invites him to do, but responds with the highest acclamation or title for Jesus anywhere in the New Testament. Thomas sees God fully revealed in Jesus. This is why Jesus is for Thomas “My Lord and my God!”
The Beatitude or blessing pronounced by Jesus on future generations’ states that having seen Jesus is not a prerequisite for faith. One must first believe in order to see.