1. You who attempt to be justified by law; you have fallen from the grace of Christ. (Gal 5:4)
    Rom 3:20, Rom 9:31-32, Rom 10:3-4, Gal 2:21

No one can be justified by works of the law. (Rom 3:20)

Rom 3:20 Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.

Israel, who obeyed the law, did not come to the law, but stumbled upon a stone to be struck. (Rom 9:31-32)

Rom 9:31 But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
32 Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;

After all, they did not obey the righteousness of God. The righteousness of God is to believe in Jesus as the Christ. With this God has fulfilled the law for us. (Rom 10:3-4)

Rom 10:3 For they being ignorant of God’s righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God.
4 For Christ is the end of the law for righteousness to every one that believeth.

If men seek to be justified by their works, Christ died in vain. (Gal 5:4, Gal 2:21)

Gal 5:4 Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.

Gal 2:21 I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain.