What does Galatians 2:12 mean?
Paul is explaining to the Galatian Christians why his authority is legitimate. This is meant to blunt the criticisms of a particular sect, the Judaizers, who claim that following the law of Moses is necessary for salvation. This is a false teaching that Paul wants the Galatians to avoid. As part of this, Paul relates how he came to be approved by the other apostles. Then, he transitions into a story about how he corrected one of those very apostles on a related issue.According to Paul, Peter had come to Antioch in Syria to visit the church there. Why did Paul oppose Peter to his face, right in front of a group of people gathered for a meal together?
For the Jewish people, who you ate with had always been a big deal. While living under the law of Moses, they never ate with Gentiles. That was forbidden. They even avoided eating with other Jewish people who were thought to be leading sinful lifestyles. That's why Jesus generated so much controversy when He ate with "tax collectors and sinners."
Paul, Peter, and the other apostles had come to an agreement that Gentiles did not need to live as Jews in order to be saved. They didn't need to be circumcised or follow the law of Moses. All were saved by grace. Many Jewish Christians, however, continued to follow the Law and Jewish practices they had grown up under.
So though the Jewish Christian leaders agreed that Gentiles could be saved, was it okay to sit at the same table and eat with them now? Because of God's grace, it was absolutely okay. They were brothers and sisters in Christ, after all. Still, it just felt wrong to many Jewish traditionalists.
Paul was Jewish and sat and ate with non-Jewish Christians all of the time. He was likely very glad to see Peter doing the same thing when he came to Antioch. But then a group of Jewish men connected to Jesus' brother James showed up. Paul calls them "the circumcision party." They absolutely did not approve of eating with Christian Gentiles. Peter knew this and left the table with the Gentiles in order to look good to this group of men. His choice would lead others to do the same.
For this, Paul will call Peter out as a hypocrite.