Matthew Henry Commentary Romans 3:19-20

"Now we know that what things soever the law saith, it speaketh to them that are under the law; that every mouth may be stopped, and all the world may be brought under the judgment of God: because by the works of the law shall no flesh be justified in his sight; for through the law [cometh] the knowledge of sin." — Romans 3:19-20 (ASV)

It is in vain to seek for justification by the works of the law. All must plead guilty. Guilty before God is a dreadful word; but no man can be justified by a law which condemns him for breaking it. The corruption in our nature will forever stop any justification by our own works.