Now we know that whatever the law says, it says to those who are under the law, so that every mouth may be silenced and the whole world held accountable to God. Therefore no one will be declared righteous in his sight by observing the law; rather, through the law we become conscious of sin" (Romans 3:19-20)
For many years I had the wrong interpretation of the Law. I always assumed that people were justified by following the Law until the time of Christ, then people we were saved by grace. I thought the Law was given as the way to God in the Old Testament. However this is not the case, Paul clearly states that the Law is what strengthened sin in us and arouses the need for a Savior.
The entire Old Testament Law can be used to point us to Christ. Paul tells us, that the Law speaks to those who are under the power of it. The purpose of the Law was to show that no one could keep it and by knowing this, it stripped every excuse that could ever be made. Every mouth is silenced in comparison to the Law, because God doesn't grade on a curve. Human comparison allows the dismissal of the severity of actions, but in contrast to the law, Paul says there is no excuse.
Because there is no excuse to those who are under the Law, and through it the world is held accountable to God, we know that the Law cannot bring us the righteousness of God. The Amplified Bible puts it this way, "For no person will be justified (made righteous, acquitted, and judged acceptable) in His sight by observing the works prescribed by the Law." ( Romans 3:20 ). And James tells us, For whoever keeps the whole law and yet stumbles at just one point is guilty of breaking all of it." ( James 2:10 ). If the Law wasn't given to make us righteous before God, why was it given?
Paul's answer... because through the Law, we become conscious of sin. We become aware of it. We recognize it. The acquaintance with the Law or condemnation of the Law, is what works us towards repentance and faith. This consciousness breaks the deception of thinking that we can be good enough to be accepted by God. The Law took away every hope of salvation except faith in a savior. This was the purpose of the Law.
This is Paul's closing argument as the prosecuting attorney. Paul finishes his case against both the Jews and the Gentiles and the impossibility of their salvation apart from Christ. He has made such a powerful case that one would think the next step is passing down the sentence of condemnation, however, now that the groundwork for the need for Christ is firmly laid, Paul will start building His case for the grace of God. What a beautiful thing!