The first book of our answer to the treatise of Celsus, entitled A True Discourse, which concluded with the representation of the Jew addressing Jesus, having now extended to a sufficient length, we intend the present part as a reply to the charges brought by him against those who have been converted from Judaism to Christianity. And we call attention, in the first place, to this special question, viz., why Celsus, when he had once resolved upon the introduction of individuals upon the stage of his book, did not represent the Jew as addressing the converts from heathenism rather than those from Judaism, seeing that his discourse, if directed to us, would have appeared more likely to produce an impression. But probably this claimant to universal knowledge does not know what is appropriate in the matter of such representations; and therefore let us proceed to consider what he has to say to the converts from Judaism.
He asserts that “they have forsaken the law of their fathers, in consequence of their minds being led captive by Jesus; that they have been most ridiculously deceived, and that they have become deserters to another name and to another mode of life.” Here he has not observed that the Jewish converts have not deserted the law of their fathers, inasmuch as they live according to its prescriptions, receiving their very name from the poverty of the law, according to the literal acceptation of the word; for Ebion signifies “poor” among the Jews, and those Jews who have received Jesus as Christ are called by the name of Ebionites.
Nay, Peter himself seems to have observed for a considerable time the Jewish observances enjoined by the law of Moses, not having yet learned from Jesus to ascend from the law that is regulated according to the letter, to that which is interpreted according to the spirit,— a fact which we learn from the Acts of the Apostles. For on the day after the angel of God appeared to Cornelius, suggesting to him “to send to Joppa, to Simon surnamed Peter,” Peter “went up into the upper room to pray about the sixth hour.
And he became very hungry, and would have eaten: but while they made ready he fell into a trance, and saw heaven opened, and a certain vessel descending unto him, as it had been a great sheet knit at the four corners, and let down to the earth; wherein were all manner of four-footed beasts, and creeping things of the earth, and fowls of the air. And there came a voice to him, Rise, Peter; kill, and eat. But Peter said, Not so, Lord; for I have never eaten anything that is common or unclean.
And the voice spoke unto him again the second time, What God has cleansed, call not common.” Now observe how, by this instance, Peter is represented as still observing the Jewish customs respecting clean and unclean animals. And from the narrative that follows, it is manifest that he, as being yet a Jew, and living according to their traditions, and despising those who were beyond the pale of Judaism, stood in need of a vision to lead him to communicate to Cornelius (who was not an Israelite according to the flesh), and to those who were with him, the word of faith.
Moreover, in the Epistle to the Galatians, Paul states that Peter, still from fear of the Jews, ceased upon the arrival of James to eat with the Gentiles, and “separated himself from them, fearing them that were of the circumcision;” and the rest of the Jews, and Barnabas also, followed the same course. And certainly it was quite consistent that those should not abstain from the observance of Jewish usages who were sent to minister to the circumcision, when they who “seemed to be pillars” gave the right hand of fellowship to Paul and Barnabas, in order that, while devoting themselves to the circumcision, the latter might preach to the Gentiles.
And why do I mention that they who preached to the circumcision withdrew and separated themselves from the heathen, when even Paul himself “became as a Jew to the Jews, that he might gain the Jews?” Wherefore also in the Acts of the Apostles it is related that he even brought an offering to the altar, that he might satisfy the Jews that he was no apostate from their law. Now, if Celsus had been acquainted with all these circumstances, he would not have represented the Jew holding such language as this to the converts from Judaism: “What induced you, my fellow citizens, to abandon the law of your fathers, and to allow your minds to be led captive by him with whom we have just conversed, and thus be most ridiculously deluded, so as to become deserters from us to another name, and to the practices of another life?”
Source: Against Celsus (New Advent)