Paul is writing to a church in crisis. Although these Galatians had learned about Christ from Paul, they were now being influenced by some missionaries who have been preaching what Paul calls a gospel so different from the one he has proclaimed that it perverts the gospel of Christ (1:6-9).
Paul reminds them of his credentials: At one time, Paul had been instrumental in the attempt to halt the inroads of the Christian message into Judaism. Then, God told him to preach to Gentiles, to tell them about Jesus Christ.
Although he began his travels without prior conference with the central church in Jerusalem, he did at a later point meet with Peter and with James, the brother of Jesus.
Paul's understanding is that Gentiles do not have to become Jews in order to be Christians. The disciples who have been upsetting the Galatians disagree. They have been trying to convince the Galatians that being a Jew is an entry requirement.
Paul himself never quit being a Jew. But, he did not restrict Christianity to Jews alone.
Paul's idea has won out over that of those false apostles to Galatia. Yet, we still are being confronted by those who think our way of being Christian is not strict enough, not close enough to the Scriptures. Or, we may be in the strict group that is preaching to those who are not living up to what appears to be very scriptural. How could they? Complainers and complainees need to spend some time with this letter.