What then shall we say? That the law is sin? By no means! Yet if it had not been for the law, I would not have known sin. For I would not have known what it is to covet if the law had not said, “You shall not covet.” (ESV)
It would be easy for Paul's readers to be confused. He spent a few verses talking about how the Law held us captive. He mentioned that the Law aroused in us every desire to do evil. The natural conclusion may be for someone to think that the Law itself is evil if it stirs up a desire in us to do evil. In today's verse Paul makes clear that the Law is by no means sin!
The Law is anything but evil. Rather, it is the perfect description of God's holy standard. It is the very thing that stops us from saying, "I did not know I was in violation of God's Law. As soon as we look at the Law we immediately feel the guilt that comes from being exposed as the actual sinners we really are.
Paul uses the illustration of coveting. In the Ten Commandments, the height of the standard of the Old Testament Law, we find a command not to covet. Paul is not saying that we never coveted until we saw the Law. He is saying that the Law exposed the fact that we were covetous sinners all along. Coveting is part of our sinful nature.
Another way of looking at the Law is that it is like a mirror. I don't like mirrors. They expose all of my imperfections and flaws. A mirror never lies. When you look into the perfect Law of God you will see all of the imperfections in your nature. The mirror cannot take away your imperfections, it only shows that they are there. The same is true with God's Law.
Thank God that we live by the Spirit, not by the Law. We are still compelled to live a holy life, but not out of fear, but rather as a love response to Christ, the fulfillment of the Law.