5 “But Thomas, one of the twelve, who is called Didymus, was not with them when Jesus came. The other disciples therefore said unto him, We have seen the Lord. But he said unto them, Except I shall see in His hands the print of the nails, and put my finger into the place of the nails, and put my hand into His side, I will not believe. And after eight days, again His disciples were within, and Thomas with them. Then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you.
Then says He to Thomas, Reach hither your finger, and behold my hands; and reach hither your hand, and put it into my side: and be not faithless, but believing. Thomas answered and said unto Him, My Lord and my God.” He saw and touched the man, and acknowledged the God whom he neither saw nor touched; but by the means of what he saw and touched, he now put far away from him every doubt, and believed the other. “Jesus says unto him, Because you have seen me, you have believed.” He says not, You have touched me, but, “You have seen me,” because sight is a kind of general sense.
For sight is also habitually named in connec tion with the other four senses: as when we say, Listen, and see how well it sounds; smell it, and see how well it smells; taste it, and see how well it savors; touch it, and see how hot it is. Everywhere has the word, See, made itself heard, although sight, properly speaking, is allowed to belong only to the eyes. Hence here also the Lord Himself says, “Reach hither your finger, and behold my hands:” and what else does He mean but, Touch and see?
And yet he had no eyes in his finger. Whether therefore it was by looking, or also by touching, “Because you have seen me,” He says, “you have believed.” Although it may be affirmed that the disciple dared not so to touch, when He offered Himself for the purpose; for it is not written, And Thomas touched Him. But whether it was by gazing only, or also by touching that he saw and believed, what follows rather proclaims and commends the faith of the Gentiles: “Blessed are they that have not seen, and yet have believed.”
He made use of words in the past tense, as One who, in His predestinating purpose, knew what was future, as if it had already taken place. But the present discourse must be kept from the charge of prolixity: the Lord will give us the opportunity to discourse at another time on the topics that remain.
Source: Tractates on the Gospel of John (New Advent)