And I have not yet spoken of the other evils which prevail among men, from which even those who have the appearance of philosophers are not speedily freed, for in philosophy there are many pretenders. Nor do I say anything on the point that many such evils are found to exist among those who are neither Jews nor Christians. Of a truth, such evil practices do not at all prevail among Christians, if you properly examine what constitutes a Christian. Or, if any persons of that kind should be discovered, they are at least not to be found among those who frequent the assemblies, and come to the public prayers, without their being excluded from them, unless it should happen, and that rarely, that some one individual of such a character escapes notice in the crowd.
We, then, are not worms who assemble together; who take our stand against the Jews on those Scriptures which they believe to be divine, and who show that He who was spoken of in prophecy has come, and that they have been abandoned on account of the greatness of their sins, and that we who have accepted the Word have the highest hopes in God, both because of our faith in Him, and of His ability to receive us into His communion pure from all evil and wickedness of life.
If a man, then, should call himself a Jew or a Christian, he would not say without qualification that God had made the whole world, and the vault of heaven for us in particular. But if a man is, as Jesus taught, pure in heart, and meek, and peaceful, and cheerfully submits to dangers for the sake of his religion, such an one might reasonably have confidence in God, and with a full apprehension of the word contained in the prophecies, might say this also: “All these things has God shown beforehand, and announced to us who believe.”
Source: Against Celsus (New Advent)