In the next place, after other Platonic declarations, which demonstrate that “the good” can be known by few, he adds: “Since the multitude, being puffed up with a contempt for others, which is far from right, and being filled with vain and lofty hopes, assert that, because they have come to the knowledge of some venerable doctrines, certain things are true.” “Yet although Plato predicted these things, he nevertheless does not talk marvels, nor shut the mouth of those who wish to ask him for information on the subject of his promises; nor does he command them to come at once and believe that a God of a particular kind exists, and that he has a son of a particular nature, who descended (to earth) and conversed with me.”
Now, in answer to this we have to say, that with regard to Plato, it is Aristander, I think, who has related that he was not the son of Ariston, but of a phantom, which approached Amphictione in the guise of Apollo. And there are several other of the followers of Plato who, in their lives of their master, have made the same statement. What are we to say, moreover, about Pythagoras, who relates the greatest possible amount of wonders, and who, in a general assembly of the Greeks, showed his ivory thigh, and asserted that he recognised the shield which he wore when he was Euphorbus, and who is said to have appeared on one day in two different cities!
He, moreover, who will declare that what is related of Plato and Socrates belongs to the marvellous, will quote the story of the swan which was recommended to Socrates while he was asleep, and of the master saying when he met the young man, “This, then, was the swan!” Nay, the third eye which Plato saw that he himself possessed, he will refer to the category of prodigies. But occasion for slanderous accusations will never be wanting to those who are ill-disposed, and who wish to speak evil of what has happened to such as are raised above the multitude.
Such persons will deride as a fiction even the demon of Socrates. We do not, then, relate marvels when we narrate the history of Jesus, nor have His genuine disciples recorded any such stories of Him; whereas this Celsus, who professes universal knowledge, and who quotes many of the sayings of Plato, is, I think, intentionally silent on the discourse concerning the Son of God which is related in Plato's Epistle to Hermeas and Coriscus. Plato's words are as follows: “And calling to witness the God of all things— the ruler both of things present and things to come, father and lord both of the ruler and cause— whom, if we are philosophers indeed, we shall all clearly know, so far as it is possible for happy human beings to attain such knowledge.”
Source: Against Celsus (New Advent)