The Blindness of Reason & Impotence of the Law

"So the words of the law are spoken, not to assert the power of the will, but to illuminate the blindness of reason, so that it may see that its own light is nothing, and the power of the will is nothing. 'By the law is knowledge of sin,' says Paul (Rom 3:20). He does not say: abolition, or avoidance, of sin. The entire design and power of the law is just to give knowledge, and that of nothing but sin; not to display or confer any power. This knowledge is not power, nor does it bring power; but it teaches and displays that there is here no power, and great weakness. What can 'knowledge of sin' be, but knowledge of our weakness and badness? He does not say: 'by the law comes knowledge of power or goodness'! All that the law does, on Paul's testimony, is to make sin known. It is from this passage that I derive my answer to you: that by the words of the law man is admonished and taught, not what he can do, but what he ought to do; that is, that he may know his sin, not that he may believe that he has any strength." - Martin Luther, The Bondage of the Will, the Revell editon, pages 158-159