After these points, Celsus proceeds to bring against the Gospel narrative a charge which is not to be lightly passed over, saying that “if Jesus desired to show that his power was really divine, he ought to have appeared to those who had ill-treated him, and to him who had condemned him, and to all men universally.” For it appears to us also to be true, according to the Gospel account, that He was not seen after His resurrection in the same manner as He used formerly to show Himself— publicly, and to all men.
But it is recorded in the Acts, that “being seen during forty days,” He expounded to His disciples “the things pertaining to the kingdom of God.” And in the Gospels it is not stated that He was always with them; but that on one occasion He appeared in their midst, after eight days, when the doors were shut, and on another in some similar fashion. And Paul also, in the concluding portions of the first Epistle to the Corinthians, in reference to His not having publicly appeared as He did in the period before He suffered, writes as follows: “For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the Scriptures; and that He was seen of Cephas, then of the twelve: after that He was seen of above five hundred brethren at once, of whom the greater part remain unto the present time, but some are fallen asleep.
After that He was seen of James, then of all the apostles. And last of all He was seen of me also, as of one born out of due time.” I am of opinion now that the statements in this passage contain some great and wonderful mysteries, which are beyond the grasp not merely of the great multitude of ordinary believers, but even of those who are far advanced (in Christian knowledge), and that in them the reason would be explained why He did not show Himself, after His resurrection from the dead, in the same manner as before that event. And in a treatise of this nature, composed in answer to a work directed against the Christians and their faith, observe whether we are able to adduce a few rational arguments out of a greater number, and thus make an impression upon the hearers of this apology.
Source: Against Celsus (New Advent)