Let it be supposed, however, that he had not read the prophecy, or that he had read it, but had been drawn away by those who misinterpreted it as not being spoken of Jesus Christ. What has he to say of the Gospel, in the narratives of which Jesus ascended up into a high mountain, and was transfigured before the disciples, and was seen in glory, when both Moses and Elias, “being seen in glory, spoke of the decease which He was about to accomplish at Jerusalem?” or when the prophet says, “We beheld Him, and He had no form nor beauty,” etc.?
And Celsus accepts this prophecy as referring to Jesus, being blinded in so accepting it, and not seeing that it is a great proof that the Jesus who appeared to be “without form” was the Son of God, that His very appearance should have been made the subject of prophecy many years before His birth. But if another prophet speak of His comeliness and beauty, he will no longer accept the prophecy as referring to Christ! And if it were to be clearly ascertained from the Gospels that “He had no form nor beauty, but that His appearance was without honour, and inferior to that of the sons of men,” it might be said that it was not with reference to the prophetic writings, but to the Gospels, that Celsus made his remarks.
But now, as neither the Gospels nor the apostolic writings indicate that “He had no form nor beauty,” it is evident that we must accept the declaration of the prophets as true of Christ, and this will prevent the charge against Jesus from being advanced.
Source: Against Celsus (New Advent)