Here are more danger signs along our path through the world — the believer’s wilderness. 1 Corinthians was a series of warnings against moral and doctrinal dangers. Galatians is about spiritual (or religious) dangers. Both books have one verse (danger sign) which is the same 1 Corinthians 5:6 and Galatians 5:9. Read Philippians 3:6 and 1 Timothy 1:15 to see what Paul had been like before he was saved. Outwardly and morally, Paul had been blameless, but spiritually he was sinning, because he was sinning against Christ. All religious or doctrinal error is against Christ. The Apostle Paul was so upset by the religious error into which the Galatian believers had fallen, that he does not say one good word to them, but plunges immediately into the subject which bothered him so much.
V.1 Paul proves his authority as an Apostle, not given to him by men, but by Jesus Christ.
V.6-9 He warns about “another gospel,” for teachers had already come with false doctrines. Even if an angel were to present any other doctrine than that which Paul was giving out, he was to be accursed. The bad doctrine that was being taught was that believers had to keep the law to keep being saved. And there are many today who try to do this. They carry Bibles and can quote many verses but they would try to put us under the law.
V.11-20 Paul did not receive the gospel from other believers, or even other apostles, but from the Lord Himself. He tells us this so that the warnings would be as from the Lord.