What does the law give us through the knowledge of our old Adam?
Through the law comes the knowledge or understanding of our old Adam—specifically, the knowledge of sin. The law is the only place this knowledge is found. It exposes the old Adamic nature rather than providing any merit, so no one can boast before God.
Les explains that by the law, verse 20, is the knowledge or understanding of our old Adam—the knowledge of sin. He says it is the only place you find it. This language is not found back in the Gospels; Jesus was dealing with those Jews under the law, but Paul, by Holy Spirit inspiration, delves into the whole human race, not just Israel. The law exposes the old Adam and sin, while salvation is not of works, lest anyone boast; it is only the work of a merciful God.