You who are trying to be justified by the law have been alienated from Christ. Paul warns here not against sin but against legalism. Whoever goes back to the law distances themselves from Christ. Falling from grace means going back to self-effort.
This is one of the strongest warnings in the New Testament, and it is directed not at sinners but at religious performers. Grace is your standing. If you take the law as your measure again, you lose access to what Christ has done.
Today you can consciously remain in grace.