Римлянам 3:20

Therefore by the deeds of--obedience to the law there shall no flesh be justified--that is, be held and treated as righteous; as is plain from the whole scope and strain of the argument. in his sight--at His bar (Psa 143:2). for by the law is the knowledge of sin--(See on Rom 4:15; Rom 7:7; and Jo1 3:4). Note, How broad and deep does the apostle in this section lay the foundations of his great doctrine of Justification by free grace--in the disorder of man's whole nature, the consequent universality of human guilt, the condemnation, by reason of the breach of divine law, of the whole world, and the impossibility of justification before God by obedience to that violated law! Only when these humiliating conclusions are accepted and felt, are we in a condition to appreciate and embrace the grace of the Gospel, next to be opened up.

The apostle, in this chapter, carries on his discourse concerning justification. He had already proved the guilt both of Gentiles and Jews. Now in this chapter, I. He answers some objections that might be made against what he had said about the Jews (Rom 3:1-8). II. He asserts the guilt and corruption of mankind in common, both Jews and Gentiles (Rom 3:9-18). III. He argues thence that justification must needs be by faith, and not by the law, which he gives several reasons for (Rom 3:19 to the end). The many digressions in his writings render his discourse sometimes a little difficult, but his scope is evident.

3:20 By doing what the law commands refers to obeying the requirements of the law of Moses. While this phrase refers to Jews, the principle extends to all people. If Jews cannot be put in right relationship with God by obeying the law God gave them, certainly other people cannot establish such a relationship through good deeds.