John the Apostle now brings up one last witness of the resurrection and shares Thomas's story of encountering the risen Lord Jesus.
24Now Thomas (also known as Didymus), one of the Twelve, was not with the disciples when Jesus came. 25So the other disciples told him, "We have seen the Lord!" But he said to them, "Unless I see the nail marks in his hands and put my finger where the nails were, and put my hand into his side, I will not believe." 26A week later his disciples were in the house again, and Thomas was with them. Though the doors were locked, Jesus came and stood among them and said, "Peace be with you!" 27Then he said to Thomas, "Put your finger here; see my hands. Reach out your hand and put it into my side. Stop doubting and believe." 28Thomas said to him, "My Lord and my God!" 29Then Jesus told him, "Because you have seen me, you have believed; blessed are those who have not seen and yet have believed" (John 20:24-29).
How did Thomas miss the appearance of Jesus that first night of the resurrection? Before we judge him too harshly, let us acknowledge that each person handles tragedy and pain in his own way. Perhaps, Thomas retreated and isolated himself by seeking solitude instead of fellowship. Everyone needs solitude at times, but when a believer is low in spirit, it is wise to receive other believers' encouragement. When we isolate ourselves, we are not aware of how vulnerable we can be and what blessings we may miss. Thomas heard the other disciples talking about Jesus' appearance with great excitement, but He would not allow himself to believe it.
How gracious the Lord was to Thomas by coming again a week later! (v.26). Jesus came up close to Thomas and invited him to check out the evidence first hand so that he would believe it! It is interesting to note that, although the Lord was not there when the disciples told Thomas of Jesus' visit, the Lord had been listening to his refusal to believe. We should always remember that God hears all that proceeds from our mouths. Nothing escapes His attention, and every idle word and action is recorded (Matthew 12:36).
Thomas was not ready to walk by faith. He was trusting only in what he could see and experience through his senses. The disciples were entering into a new relationship with Jesus, one that required them to walk by faith, not by sight (2 Corinthians 5:7). Thomas wanted to see and feel before he would believe that Christ had indeed risen. When the Lord invited Thomas to touch the nail marks in His hands, he fell to his knees, saying, "My Lord and my God!"
To Thomas' credit, once he saw Jesus, he did not hold back but immediately worshiped Him. He finally entered into the blessing and joy that the other disciples experienced. Not all believers will have evidence given to their senses. Like Thomas, some people are waiting for absolute proof before putting faith in Christ. Some will not take a step of faith because they are waiting for a supernatural sign or a prophetic word from the Lord. On occasion, God may unusually give a person confirmation, but we should step out in faith on God's objective word and the testimony of the Holy Spirit inside us. We must live by faith and not by sight. Jesus said to Thomas, "Because you have seen me, you have believed; blessed are those who have not seen and yet have believed" (John 20:29). If you are a believer, Jesus was speaking about you!
In the fictional book by C.S. Lewis, The Screwtape Letters, Lewis writes of a training session between a seasoned senior demon and a young demon. The young demon requires advice on his first assignment to disrupt and destroy a new Christian's faith. C.S. Lewis offers interesting insight as to a Christian learning to walk by faith and not by sight:
"He [God] wants them to learn to walk and must therefore take away His hand; and if only the will to walk is really there He is pleased even with the stumbles. Do not be deceived, Wormwood. Our cause is never more in danger than when a human, no longer desiring, but still intending, to do our enemy's will, looks around upon a universe from which every trace of Him seems to have vanished, and asks why he has been forsaken, and still obeys."
Those who have not perceived by the five senses but have still believed express the kind of faith God is looking for. The African impala gives us a perfect illustration of the difference between our sense knowledge and faith. The impala can be kept in an enclosure with a wall only three feet high, even though these animals can jump to a height of over ten feet and cover a distance of more than thirty feet with a single bound. However, the impalas will not jump unless they can see where their feet will land. Faith is the ability to trust what we cannot see and leap out of whatever barriers keep us bound to the realm of the senses. Thomas is the last of the disciples John presents as a testimony to you and me to help us believe and trust in Christ. Keith Thomas.
Taken from the series on the Gospel of John, study 41: Jesus Appears to Mary and the Disciples
 C.S. Lewis. The Screwtape Letters. New York, N.Y. The Macmillan Co., 1959, page 47.