What does Galatians 5:10 mean?
Someone has been teaching the false idea that Gentile Christians must get circumcised and begin to follow the law in order to truly be made right before God (Galatians 2:4). That teaching goes flatly against Paul's message that salvation is by faith alone in Christ alone. Anything added to faith in Christ makes faith in Christ meaningless (Galatians 5:2–4; Romans 6:11). Such teaching cannot be allowed to linger among them. Paul has asked pointedly who the person is among them who is responsible for steering them in the wrong direction (Galatians 5:7).Now Paul declares he is confident "in the Lord" that the Galatians will not ultimately accept this person's false teaching. God has given Paul confidence to believe the Galatians will get back up and keep running in the right direction together.
He goes further: Paul is confident that the person troubling them with false teaching about the grace of God through faith in Christ will pay the penalty for that sin. Clearly, Paul is serious. This person is not guilty of a minor infraction; he is luring people away from the grace of God. He will face consequences from God Himself (Galatians 1:6–9).