What does Galatians 2:14 mean?
Paul is describing an incident between himself and Peter, which supports his claims to apostolic authority. Paul knew what Peter believed, that Gentiles were fully accepted by God's grace through faith in Christ, that their sins were covered by Jesus' death on the cross. In fact, Peter believed that's how Jewish people were saved, as well. But Peter got scared when some men who still thought it was wrong to eat with Gentiles walked in and found him eating at a table with Gentiles. Peter got up and left the table, maybe not expecting all of the other Jewish people at the table to get up and follow his hypocritical example.Paul had seen enough. He confronted Peter right out in the open in front of everyone gathered together to eat. Paul didn't confront Peter out of a sense of outrage for his Gentile friends. He confronted Peter openly for the sake of the truth of the gospel. Peter's actions were teaching everyone present that Christians came in two flavors: Jewish and Gentile. That was not the gospel. Everyone is saved by trusting in God's grace to forgive sin through Jesus' death on the cross. Nobody is saved by following the Law.
Paul used a question to challenge Peter: You're a Jew, and you were living like a Gentile before these guys came in. How can you now force Gentiles to live according to Jewish Law and traditions in order to be seen as saved and equal with Jewish Christians before God?
Peter's response is not recorded, but it is not needed. God Himself had commanded Peter to overcome his attachment to the Law and the customs of Judaism in order to accept and receive the Gentiles (Acts 10). Often, our real-world actions lag behind our bedrock beliefs. We should be glad to have someone like Paul rebuke us to get us back on the right track.