What does Galatians 1:18 mean?
Was Paul really qualified to be called an apostle of Jesus Christ? Wasn't he just a convert to Jesus who had been trained by the other apostles? Is his teaching trustworthy? These are the questions a particular group of false teachers were asking the Galatian Christians about Paul. Called "Judaizers," they taught that Gentiles must still follow the law of Moses to be saved. The Galatian Christians were being influenced by these deceivers.To defend the truth of the gospel of salvation by grace alone, Paul has been defending himself. He has described how, after God revealed Christ to him and called him to preach to the Gentiles (Acts 9:1–22), he did not receive training from the other apostles. Instead, he went off by himself for three years. This time, apparently, is when he came to understand the gospel of Jesus that he preached in Galatia.
Now he reveals that he did interact with Peter, using the untranslated Aramaic form of his nickname: Cephas. Even at that time, Peter was considered to be the chief of the apostles. Paul spent fifteen days with Peter in Jerusalem before having to run for his life for preaching about Jesus (Act 9:29). His point is that those fifteen days with Peter were not spent in training or commissioning by Peter. Paul had already received that from the Lord.