Although Jesus was only a single individual, He was nevertheless more things than one, according to the different standpoint from which He might be regarded; nor was He seen in the same way by all who beheld Him. Now, that He was more things than one, according to the varying point of view, is clear from this statement, “I am the way, and the truth, and the life;” and from this, “I am the bread;” and this, “I am the door,” and innumerable others. And that when seen He did not appear in like fashion to all those who saw Him, but according to their several ability to receive Him, will be clear to those who notice why, at the time when He was about to be transfigured on the high mountain, He did not admit all His apostles (to this sight), but only Peter, and James, and John, because they alone were capable of beholding His glory on that occasion, and of observing the glorified appearance of Moses and Elijah, and of listening to their conversation, and to the voice from the heavenly cloud.
I am of opinion, too, that before He ascended the mountain where His disciples came to Him alone, and where He taught them the beatitudes, when He was somewhere in the lower part of the mountain, and when, as it became late, He healed those who were brought to Him, freeing them from all sickness and disease, He did not appear the same person to the sick, and to those who needed His healing aid, as to those who were able by reason of their strength to go up the mountain along with Him.
Nay, even when He interpreted privately to His own disciples the parables which were delivered to the multitudes without, from whom the explanation was withheld, as they who heard them explained were endowed with higher organs of hearing than they who heard them without explanation, so was it altogether the same with the eyes of their soul, and, I think, also with those of their body. And the following statement shows that He had not always the same appearance, viz., that Judas, when about to betray Him, said to the multitudes who were setting out with him, as not being acquainted with Him, “Whomsoever I shall kiss, the same is He.” And I think that the Saviour Himself indicates the same thing by the words: “I was daily with you, teaching in the temple, and you laid no hold on Me.” Entertaining, then, such exalted views regarding Jesus, not only with respect to the Deity within, and which was hidden from the view of the multitude, but with respect to the transfiguration of His body, which took place when and to whom He would, we say, that before Jesus had “put off the governments and powers,” and while as yet He was not dead unto sin, all men were capable of seeing Him; but that, when He had “put off the governments and powers,” and had no longer anything which was capable of being seen by the multitude, all who had formerly seen Him were not now able to behold Him. And therefore, sparing them, He did not show Himself to all after His resurrection from the dead.
Source: Against Celsus (New Advent)