By Works Of The Law - Romans 3:19-20

Romans 3:19-20 ESV 

Now we know that whatever the law says it speaks to those who are under the law, so that every mouth may be stopped, and the whole world may be held accountable to God. For by works of the law no human being will be justified in his sight, since through the law comes knowledge of sin.

The law was given to a particular people to bring it to the whole world. That particular people demonstrated the inability of man to comply, and therefore the need for a redeemer. The knowledge of sin includes accountability.  Their failure provided the light and pathway to God.  We learn that our best effort can only fall short of the righteousness of God.  

Every mouth will be silenced before the law, for through the law comes the knowledge of sin.