After these assertions, he takes from the Gospel of Matthew, and perhaps also from the other Gospels, the account of the dove alighting upon our Saviour at His baptism by John, and desires to throw discredit upon the statement, alleging that the narrative is a fiction. Having completely disposed, as he imagined, of the story of our Lord's birth from a virgin, he does not proceed to deal in an orderly manner with the accounts that follow it; since passion and hatred observe no order, but angry and vindictive men slander those whom they hate, as the feeling comes upon them, being prevented by their passion from arranging their accusations on a careful and orderly plan.
For if he had observed a proper arrangement, he would have taken up the Gospel, and, with the view of assailing it, would. have objected to the first narrative, then passed on to the second, and so on to the others. But now, after the birth from a virgin, this Celsus, who professes to be acquainted with all our history, attacks the account of the appearance of the Holy Spirit in the form of a dove at the baptism. He then, after that, tries to throw discredit upon the prediction that our Lord was to come into the world.
In the next place, he runs away to what immediately follows the narrative of the birth of Jesus— the account of the star, and of the wise men who came from the east to worship the child. And you yourself may find, if you take the trouble, many confused statements made by Celsus throughout his whole book; so that even in this account he may, by those who know how to observe and require an orderly method of arrangement, be convicted of great rashness and boasting, in having inscribed upon his work the title of A True Discourse,— a thing which is never done by a learned philosopher.
For Plato says, that it is not an indication of an intelligent man to make strong assertions respecting those matters which are somewhat uncertain; and the celebrated Chrysippus even, who frequently states the reasons by which he is decided, refers us to those whom we shall find to be abler speakers than himself. This man, however, who is wiser than those already named, and than all the other Greeks, agreeably to his assertion of being acquainted with everything, inscribed upon his book the words, A True Discourse!
Source: Against Celsus (New Advent)