Notice how simple the words are: “Through the law comes knowledge of sin”; yet they alone are powerful enough to confound and overthrow free choice. For if it is true that when left to itself it does not know what sin and evil are—as he says both here and in Romans 7:7: “I should not have known that covetousness is sin if the law had not said, ‘You shall not covet,’ ”—how can it ever know what righteousness and goodness are? And if it does not know what righteousness is, how can it strive toward it? If we are unaware of the sin in which we were born, in which we live, move, and have our being, or rather, which lives, moves, and reigns in us, how should we be aware of the righteousness that reigns outside of us in heaven? These statements make complete and utter nonsense of that wretched thing, free choice.
This being so, Paul speaks with full confidence and authority when he declares: “But now the righteousness of God is manifested apart from law, although the law and the prophets bear witness to it; the righteousness of God, I say, through faith in Jesus Christ for all and upon all who believe in him. For there is no distinction; since all have sinned and fallen short of the glory of God, they are justified by his grace as a gift, through the redemption which is in Christ Jesus, whom God put forward as an expiation by his blood,” etc. [Romans 3:21–25]. Paul’s words here are absolute thunderbolts against free choice.
Martin Luther, “On the Bondage of the Will” (LW 33:262-263)