What does Galatians 2:15 mean?

It is unclear from the text whether the words here are a continuation of Paul's rebuke of Peter, as given in the previous verse, or whether this is simply Paul expounding the point of his story. In either case, Paul begins here to make the major point of his letter to the Galatians: Every person is justified—"made just or acceptable"—before God by faith and not by works or the Law.

Paul begins by saying that he and Peter are both Jewish by birth. They seemingly had the advantage of being born into the nation of the chosen people of God, blessed by God with the Law and the sacrificial system. It offered a way to be right with God as a people. They also had the advantage of not being born as "Gentile sinners," born outside of God's chosen people with limited opportunities to be saved and welcomed by Him.

As Paul will beautifully explain in the following verses, Jesus changed everything. More accurately, He brought everything into focus. The gospel truth Paul had been preaching and that Peter himself agreed with was that nobody can be saved by following the works of the Law. We are only justified by faith in Christ.