Tell thy conscience that it cannot manage any evidence to the purpose that thou art free from the condemning power of sin, whilst thy unmortified lust lies in thy heart; so that, perhaps, the law may make good its plea against thee for a full dominion, and then thou art a lost creature. Wherefore it is best to ponder to the utmost what it hath to say.
Assuredly, he that pleads in the most secret reserve of his heart that he is freed from the condemning power of the law, thereby secretly to countenance himself in giving the least allowance unto any sin or lust, is not able, on gospel grounds, to manage any evidence, unto any tolerable spiritual security, that indeed he is in a due manner freed from what he so pretends himself to be delivered.
– John Owen –
from The Mortification of Sin in Believers, volume 6 of Works, page 57
The Essential Owen 