And yet, against his will, Celsus is entangled into testifying that the world is comparatively modern, and not yet ten thousand years old, when he says that the Greeks consider those things as ancient, because, owing to the deluges and conflagrations, they have not beheld or received any memorials of older events. But let Celsus have, as his authorities for the myth regarding the conflagrations and inundations, those persons who, in his opinion, are the most learned of the Egyptians, traces of whose wisdom are to be found in the worship of irrational animals, and in arguments which prove that such a worship of God is in conformity with reason, and of a secret and mysterious character.
The Egyptians, then, when they boastfully give their own account of the divinity of animals, are to be considered wise; but if any Jew, who has signified his adherence to the law and the lawgiver, refer everything to the Creator of the universe, and the only God, he is, in the opinion of Celsus and those like him, deemed inferior to him who degrades the Divinity not only to the level of rational and mortal animals, but even to that of irrational also!— a view which goes far beyond the mythical doctrine of transmigration, according to which the soul falls down from the summit of heaven, and enters into the body of brute beasts, both tame and savage!
And if the Egyptians related fables of this kind, they are believed to convey a philosophical meaning by their enigmas and mysteries; but if Moses compose and leave behind him histories and laws for an entire nation, they are to be considered as empty fables, the language of which admits of no allegorical meaning!
Source: Against Celsus (New Advent)