Against Celsus 3.12

Then, since as if accusing our teaching he reproaches us with the heresies in Christianity, saying, “But having spread into a multitude, they are split and divided again and again, and each wish to have their own factions”; and he says that “being again divided by their multitude they refute one another, still sharing, so to speak, only one thing, if indeed they share it, the name; and this alone they are nevertheless ashamed to abandon; but in everything else they are ranged on different sides”: to this too we shall say that there have been different schools in no matter whose origin is not serious and useful to life. For since medicine is useful and necessary to the human race, and there are many questions in it about the method of treating bodies, schools are admittedly found in medicine among the Greeks, and I think also among the barbarians, as many (at least) as profess to use medicine. Again, since philosophy, which professes truth and the knowledge of what exists, sets forth how one ought to live and tries to teach what is beneficial to our race, and the questions it investigates allow great divergence, a great many schools have formed in philosophy, some more famous than others. Judaism too had an occasion for the rise of sects in the different interpretation of the writings of Moses and the words of the prophets. So, since Christianity appeared something worthy of respect to people, not only, as Celsus thinks, to the more servile, but also to many of the learned among the Greeks, heresies necessarily arose, not at all because of factions and contentiousness, but because many of the learned too were eager to understand the teachings of Christianity. From this it followed that, as they interpreted differently the words all believed to be divine, there arose heresies named after those who admired the origin of the teaching but were moved, in one way or another, by certain plausible arguments to disagree with one another. But no one would reasonably shun medicine because of its schools, nor would anyone who aims at what is fitting hate philosophy, making its many schools a pretext for hating it. So neither should the sacred books of Moses and the prophets be condemned because of the sects among the Jews.