For before certain men came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them who were of the circumcision.
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Gaius Marius Victorinus
AD 400
But in what way was Peter sinning? He had not adopted this ruse to bring in the Jews, meeting them on their own terms (which Paul himself had done and glories in having done, meeting the Jews on their own terms but for their profit). Rather, the sin of Peter lay in the fact that he withdrew, through fear of those who were of the circumcision. –.
Perhaps indeed he would at this point have kept silent about the sin that he says he reproved in Peter, for it was enough that Peter had been corrected by popular reproof and Paul’s open accusation. But it is profitable and extremely requisite for this letter. He has two reasons for relating the incident. First, his own gospel was not reproved, and he himself, when he reproved Peter, heard no reproof from Peter. Next, this too, as I said, was extremely pertinent: it is because the Galatians thought that they needed to add to the principles of the gospel to obtain life … that this letter is being written to them. Hence it is very good to tell the story, because it is this very fault that was reproved by Paul in Peter and by the people also. In this way it follows that the Galatians too are sinning. –.
But they themselves, while knowing the same God, continued in the ancient observances; so that even Peter, fearing also lest he might incur their reproof, although formerly eating with the Gentiles, because of the vision, and of the Spirit who had rested upon them, yet, when certain persons came from James, withdrew himself, and did not eat with them. And Paul said that Barnabas likewise did the same thing.
He was not afraid of his own endangerment; for one who had no fear at the beginning would have all the less at that time. Rather, he feared their apostasy. Just as Paul himself says to the Galatians, “I am afraid I have labored over you in vain.”
From those who came down from Jerusalem. “Because he was afraid of those from the circumcision.” In other words, that he might not scandalize them, and might not suffer anything terrible on their account.
Paul, however, censures Peter for not walking straightforwardly according to the truth of the gospel. No doubt he blames him; but it was solely because of his inconsistency in the matter of "eating".
which he varied according to the sort of persons (whom he associated with) "fearing them which were of the circumcision"