Immediately after this, Celsus, assailing the contents of the first book of Moses, which is entitled “Genesis,” asserts that “the Jews accordingly endeavoured to derive their origin from the first race of jugglers and deceivers, appealing to the testimony of dark and ambiguous words, whose meaning was veiled in obscurity, and which they misinterpreted to the unlearned and ignorant, and that, too, when such a point had never been called in question during the long preceding period.”
Now Celsus appears to me in these words to have expressed very obscurely the meaning which he intended to convey. It is probable, indeed, that his obscurity on this subject is intentional, inasmuch as he saw the strength of the argument which establishes the descent of the Jews from their ancestors; while again, on the other hand, he wished not to appear ignorant that the question regarding the Jews and their descent was one that could not be lightly disposed of. It is certain, however, that the Jews trace their genealogy back to the three fathers, Abraham, Isaac, and Jacob.
And the names of these individuals possess such efficacy, when united with the name of God, that not only do those belonging to the nation employ in their prayers to God, and in the exorcising of demons, the words, “God of Abraham, and God of Isaac, and God of Jacob,” but so also do almost all those who occupy themselves with incantations and magical rites. For there is found in treatises on magic in many countries such an invocation of God, and assumption of the divine name, as implies a familiar use of it by these men in their dealings with demons.
These facts, then— adduced by Jews and Christians to prove the sacred character of Abraham, and Isaac, and Jacob, the fathers of the Jewish race— appear to me not to have been altogether unknown to Celsus, but not to have been distinctly set forth by him, because he was unable to answer the argument which might be founded on them.
Source: Against Celsus (New Advent)