What does Galatians 2:11 mean?

This verse brings a sudden shift in Paul's reported relationship with the other apostles, specifically Peter. This example becomes the springboard Paul uses to emphasize his message that salvation comes by faith, not by works. In order to defend himself against the charges from his accusers that he was not a full apostle, but merely a student of the other apostles—like Peter—Paul has outlined his relationship with them.

First, God was the one who revealed Jesus to Paul. He was not converted by the preaching of any other teacher. Second, after Paul's conversion, he was not trained by the apostles. He went off by himself and learned about Christ from Christ. He did meet with Peter and Jesus' brother James briefly, after already developing his understanding of the gospel, and then ministered on his own in Syria and Cilicia. Paul's point to his accusers was that he was a full apostle, by God's own calling and grace, and not because of any close association with the apostles in and around Jerusalem.

In the previous verses, Paul also showed he was preaching the same gospel truth as the other apostles. In fact, Peter, James, and John had given to him and Barnabas their full approval.

Now Paul will show that he remained independent of Peter, referred to here as Cephas, the original Aramaic version of the name given to him by Jesus. Paul was not under Peter's authority. In fact, when Peter came to Antioch in Syria, where Paul lived, Paul opposed him to his face over a serious issue, about which Paul knew Peter was dead wrong. Paul exercised his own God-given authority as apostle with Peter. How could he have done that if he was not a full apostle himself?