Galatians 2:12

Before that certain came from James. Men sent from Jerusalem by James, who stood now at the head of that church.

He used to eat with the Gentiles. See Ac 11:3. Peter had no scruples about eating with Gentile Christians; but many of the Jewish Christians did. Hence he did before the messengers came from James what he refused to do after they came, "separating himself" from the Gentile Christians at Antioch.
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