Romans 7:16

If then I do that which I would not, I consent unto the law that it is good.

When a person does what he does not want to do, that very conflict shows he agrees that God's law is good. Recognizing the goodness of the law gives no power to obey it, leaving the one who sees it still carnal and sold under sin. In that condition he longs for a purity and righteousness that he cannot attain by himself.