Grace is the benevolence of God bestowed on sinful men who deserve punishment for rebellion against the one true God, creator of heaven and earth. Grace is the king’s pardon to men blind to their own sinful condition, (John 3:3) and need to be awakened to their desperate need of Him.
God gives eternal life freely as a gift by grace, to those who cannot obtain it on their own, which is why Paul would not “frustrate” set aside, disannul, or make void because of its surpassing value, the grace of God. If men could obtain righteousness by the law then Christ need not die, and died in vain.
The person who seeks to earn favor with God by obeying His law sets aside the sacrifice of His Son.