Paul responds, “Certainly not!” then explains:  “I would not have known what sin was except through the law.”  The law exposes sin.  It declares a standard and holds us accountable.  Paul, as a religious man, tried hard to live by the law, and thought he was doing ok. 

Suddenly, when he read, “Do not covet,” his conscience was pricked, reminding him of every kind of covetous desire.  He began to realize that he coveted many things. Though intellectually aware of the law, he obeyed it perfunctorily.  Then, the law, like a switch, turned the lights on in his heart.  Suddenly he remembered his prior life: “Once I was alive apart from law.”  He was admitting in verse 9, “I was a happy sinner, oblivious of my own failure, motivationally and behaviorally.” 

By exposing him to his real self the law did a good thing.  It couldn’t change him, but it showed him his need for a change in his life.  It prepared him to receive life as a gift.  By exposing our shortcomings the law points us to our need to depend upon God’s grace.  The law can’t save us nor grow us, but it exposes us to a righteous standard that is consistent with God’s character.