After the above remarks he proceeds as follows: “Let no one suppose that I am ignorant that some of them will concede that their God is the same as that of the Jews, while others will maintain that he is a different one, to whom the latter is in opposition, and that it was from the former that the Son came.” Now, if he imagine that the existence of numerous heresies among the Christians is a ground of accusation against Christianity, why, in a similar way, should it not be a ground of accusation against philosophy, that the various sects of philosophers differ from each other, not on small and indifferent points, but upon those of the highest importance?
Nay, medicine also ought to be a subject of attack, on account of its many conflicting schools. Let it be admitted, then, that there are among us some who deny that our God is the same as that of the Jews: nevertheless, on that account those are not to be blamed who prove from the same Scriptures that one and the same Deity is the God of the Jews and of the Gentiles alike, as Paul, too, distinctly says, who was a convert from Judaism to Christianity, “I thank my God, whom I serve from my forefathers with a pure conscience.” And let it be admitted also, that there is a third class who call certain persons “carnal,” and others “spiritual,”— I think he here means the followers of Valentinus—yet what does this avail against us, who belong to the Church, and who make it an accusation against such as hold that certain natures are saved, and that others perish in consequence of their natural constitution? And let it be admitted further, that there are some who give themselves out as Gnostics, in the same way as those Epicureans who call themselves philosophers: yet neither will they who annihilate the doctrine of providence be deemed true philosophers, nor those true Christians who introduce monstrous inventions, which are disapproved of by those who are the disciples of Jesus. Let it be admitted, moreover, that there are some who accept Jesus, and who boast on that account of being Christians, and yet would regulate their lives, like the Jewish multitude, in accordance with the Jewish law—and these are the twofold sect of Ebionites, who either acknowledge with us that Jesus was born of a virgin, or deny this, and maintain that He was begotten like other human beings—what does that avail by way of charge against such as belong to the Church, and whom Celsus has styled “those of the multitude?” He adds, also, that certain of the Christians are believers in the Sibyl, having probably misunderstood some who blamed such as believed in the existence of a prophetic Sibyl, and termed those who held this belief Sibyllists.
Source: Against Celsus (New Advent)