What does Galatians 1:12 mean?

Paul's authority was under attack. Paul is writing to Galatian Gentiles who initially received the gospel as he taught it to them. Afterwards, a group called the Judaizers came along to claim Paul was wrong. According to these false teachers, it wasn't enough to just receive God's grace through faith in Christ; you had to follow the law of Moses to truly be saved.

The Judaizers apparently argued that Paul was not one of the original 12 apostles trained by Jesus during his time on earth. Paul is defending himself, insisting that he received the truth of the gospel in a direct revelation from Jesus as well.

In the previous verse, he said that what he taught the Galatians about Jesus was not a man-invented religion. Now he goes on: I didn't hear it from another person. I wasn't taught about it by someone else, as the Galatians were taught about it by him. Paul did not back down: He received this gospel truth that he taught to them straight from Jesus Himself through special revelation.