John 20:27

Put in thy finger hither. Christ, to shew he knew all things, made use of the very same words in which St. Thomas had expressed his incredulous dispositions. Our blessed Redeemer would have the mark of the spear, and the prints of the nails to remain in his glorified body, to convince them it was the same body: and that they might be for ever marks of his victory and triumph over sin and the devil. The evangelist does not say, that St. Thomas went and touched Christ's body, though it is very probable he did as he was ordered. But how could a body that entered in, when the doors were shut, be felt, or be palpable? St. John Chrysostom[2] answers, that Christ at that time permitted his body to be palpable, and to resist another body, to induce St. Thomas to believe the resurrection; and that when he pleased, his body could not be felt. In like manner, his body was either visible or invisible, as he had a will it should be. In fine, he could eat in their sight, though he stood not in need of any nourishment. See St. Augustine.

Be not incredulous, but faithful. In the Greek, be not an unbeliever, but a believer. --- My Lord, and my God; that is, I confess thee to be my Lord, and my God; and with the Greek article, to be him, that is, the Lord, and the God. (Witham)