Acts 15:1 Now some men came down from Judea and began to teach the brothers, “Unless you are circumcised according to the custom of Moses, you cannot be saved.” NET
The word “circumcision” is shorthand for following the law. There are people saying that Paul is wrong and that grace alone is not enough to save you. Note that when we speak of grace, we are talking about something that God has done for us rather than something we have done ourselves. It is as if we have been judged and found “not guilty”, even though we really are guilty.
Where we see “ought to” or “need to” in the Bible, that is law. In response to the rich young ruler, Jesus rattles off commandments to which the young man replies that he has done all of that and has essentially followed the law his whole life. When Jesus follows up and tells him that to be perfect, he must give everything away and follow Him, the young ruler walks away. No matter how good he might think he is at following the law, this last commandment from Jesus is simply too much for him to do and as a result, he falls short.
Romans 3:19 Now we know that whatever the law says, it says to those who are under the Law, so that every mouth may be silenced and the whole world held accountable to God. 20Therefore no one will be justified in His sight by works of the law. For the law merely brings awareness of sin. 21 But now, apart from the law, the righteousness of God has been revealed, as attested by the Law and the Prophets. 22 And this righteousness from God comes through faith in Jesus Christ to all who believe. There is no distinction, 23 for all have sinned and fall short of the glory of God, 24 and are justified freely by His grace through the redemption that is in Christ Jesus. BSB
The law shows our need for Christ, as no matter how “good” we may appear on the outside, it is a different story on the inside, as we can’t do anything to deserve salvation.
Galatians 1:6 I am amazed how quickly you are deserting the One who called you by the grace of Christ and are turning to a different gospel— 7 which is not even a gospel. Evidently some people are troubling you and trying to distort the gospel of Christ. 8 But even if we or an angel from heaven should preach a gospel contrary to the one we preached to you, let him be under a curse! 9 As we have said before, so now I say again: If anyone is preaching to you a gospel contrary to the one you embraced, let him be under a curse! BSB
Paul has come back from his first mission trip feeling pretty good about things and the churches that he has planted and now he has word that people are questioning him and what he has taught. In Paul’s mind, the Gospel is so well defined that he immediately knows these new teachings to be false. There can be a question about who is “One” (or “Him”) in verse six as some translations will not capitalize these under the thinking that it is really referring to Paul. But in Paul’s mind, these people in Galatia aren’t abandoning him, they are abandoning God!
The Judaizers, like Paul, are trying to get a wedding garment but have managed to come up with a different Gospel. We see this today, for example, in the prosperity preaching where God becomes the means by which we can all become healthy and wealthy. (Provided, among other things, that we have enough faith and give enough money). Then there are churches that are more focused on being PC than being focused on JC. Some, like the Judaizers, add stumbling blocks to the Gospel while others ignore the parts of the Gospel that they (or the outside world) find troublesome or offensive. Paul’s answer to these churches today would be the same as his answer to the Galatians in that anyone preaching a false gospel is cursed. Paul is comfortable with that statement because the stakes are just that high.
Galatians 5:2 Listen! I, Paul, tell you that if you let yourselves be circumcised, Christ will be of no benefit to you at all! 3 And I testify again to every man who lets himself be circumcised that he is obligated to obey the whole law. 4 You who are trying to be declared righteous by the law have been alienated from Christ; you have fallen away from grace! NET
Recall that in Acts 15, the Judaizers are saying that you must be a Jew to follow Christ. Paul’s response is that if you go down that path, Christ is of no value to you and as a result, you have fallen from grace! In other words, once you go down the path of following the law, you have let go of the life preserver and have to obey the whole law (remembering, of course, that God doesn’t grade on a curve). You have fallen from grace because at this point you are thinking you can do it on your own. Paul is now going to move on to why you should listen to him.
Galatians 1:11 Now I want you to know, brothers and sisters, that the Gospel I preached is not of human origin. 12 For I did not receive it or learn it from any human source; instead I received it by a revelation of Jesus Christ NET
Whenever you see “brothers and sisters” (or brethren), it indicates that this is a conversation among fellow believers. Note that by using this term, Paul still regards these people as Christians despite the fact that the Galatians are being deceived and are on the brink of losing everything.
Paul makes a bold claim in that he received his Gospel by revelation from Jesus. The act of revelation is like opening a curtain to reveal something you didn’t know (and couldn’t figure out on your own without it being made known to you). He eventually goes to Jerusalem where his preaching matches what the other apostles are preaching although Paul didn’t get his teaching from any of them. In verse 12, we see the wording “of” Jesus – so is this a revelation from Jesus or about Jesus? Paul has the knowledge of Jesus after his Damascus experience and the three years in the wilderness but as he tells us here, his Gospel did not come from humans. Rather, his knowledge comes from the current (and Risen) Jesus. It sounds a little presumptuous for Paul to claim apostleship to many, especially considering his past as a persecutor of Christians and that unlike John and Peter, he wasn’t an eyewitness to the worldly ministry of Jesus. This is something he has to constantly address.