What does Galatians 1:11 mean?

Paul is writing to the Christians in Galatia to stop them from following the false teaching of a group known as the Judaizers. This group came in after the Galatians believed in the true gospel message of free grace through faith in Christ and after Paul left. They were teaching that these new Gentile Christians must follow the law of Moses to truly be saved.

One of their arguments was that Paul was not a "real" apostle. He was not one of the 12 originally chosen by Jesus during His time on earth. Given that, they seem to ask, how could his teaching be trusted?

Paul understood that people had to be able to trust his authority as a genuine apostle, one actually sent out by Christ Himself, if they were to believe the truth that he taught them. So he begins a defense of his authority as an apostle in this verse.

The first argument he makes is that what he preached to them is not something dreamed up by some human being. It's not "man's gospel." In other words, Paul is not just passing along some religious teaching he picked up from other people. In the following verses, he will make the case that what he teaches was given to him directly from Christ.