Albert Barnes on Romans 7:16

I consent unto the law. The very struggle with evil shows that it is not loved, or approved, but that the law which condemns it is really loved. Christians may here find a test of their piety. The fact of struggling against evil--the desire to be free from it, and to overcome it, the anxiety and grief which it causes--is an evidence that we do not love it, and that therefore we are the friends of God. Perhaps nothing can be a more decisive test of piety than a long-continued and painful struggle against evil passions and desires in every form, and a panting of the soul to be delivered from the power and dominion of sin.