The story of Thomas 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!”