2 Let no one then, Brethren, say that our Lord Jesus Christ does not those things now, and on this account prefer the former to the present ages of the Church. In a certain place indeed the same Lord prefers those who “do not see, and yet believe,” to them who see and therefore believe. For even at that time so irresolute was the infirmity of His disciples, that they thought that He whom they saw to have risen again must be handled, in order that they might believe.
It was not enough for their eyes that they had seen Him, unless their hands also were applied to His limbs, and the scars of His recent wounds were touched; that that disciple who was in doubt, might cry out suddenly when he had touched and recognised the scars, “My Lord and my God.” The scars manifested Him who had healed all wounds in others. Could not the Lord have risen again without the scars? Yes, but He knew the wounds which were in the hearts of His disciples, and to heal them He had preserved the scars on His own Body.
And what said the Lord to him who now confessed and said, “My Lord and my God”? “Because you have seen,” He said, “you have believed; blessed are they who do not see, and yet believe.” Of whom spoke He, Brethren, but of us? Not that He spoke only of us, but of those also who shall come after us. For after a little while when He had departed from the sight of men, that faith might be established in their hearts, whosoever believed, believed, though they saw Him not, and great has been the merit of their faith; for the procuring of which faith they brought only the movement of a pious heart, and not the touching of their hands.
Source: Sermons on Selected Lessons of the New Testament (New Advent)