Gal 5:4 For if you are trying to make yourselves right with God by keeping the law, you have been cut off from Christ! You have fallen away from God’s grace. (NLT)
In Gal 5:1, Paul is making a distinction between law and grace. One enslaves and the other gives freedom. Here the Galatians brethren began to add some aspect of the the law and traditions as prequisite to salvation. Paul in verse 1 reminds them they were freed from the law by grace through faith in Christ and should not put that bondage on themselves and others because it nullifies (voids) grace.
He begins to make his case in vs. “2 Look: I, Paul, say to you that if you accept circumcision, Christ will be of no advantage to you.” In summary, Christ is not advategious to you bcause the law cancels the grace we all desperately need.
Second case vs “3. I testify again to every man who accepts circumcision that he is obligated to keep the whole law.” Here he states again that if you are seeking to be justified by the law, then you must keep all of them (words, thoughts and deeds). Jesus told the rich young ruler in Mat 19:21 who was destined to have eternal life by keeping the law that he needed to be perfect. It was not long before he realized that he loved his money more than God. He broke the first, second and third commandment.
Having made his case on the first three verses, now we can understand this verse “For if you are trying to make yourselves right with God by keeping the law, you have been cut off from Christ! You have fallen away from God’s grace. (Gal 5:4 NLT)” This verse is not for the saved backsliding but those who would chose to be saved by mashing law and grace. In other words, if you add law as prequisite to salvation, you are cut off from Christ, you cannot be saved because salvation is by grace alone, through faith alone in Christ alone. If this is not how you view salvation, you have fallen from grace because this is the only grace that saves “So we are made right with God through faith and not by obeying the law. (Rom 3:28 NLT)”
Any person who adds any thing to Christ for salvation has fallen from grace