Sin aims always at the utmost; every time it rises up to tempt or entice, might it have its own course, it would go out to the utmost sin in that kind. Every unclean thought or glance would be adultery if it could…every rise of lust, might it have its course, would come to the height of villany: it is like the grave that is never satisfied. And herein lies no small share of the deceitfulness of sin, by which it prevails to the hardening of men, and so to their ruin (Heb. 3:13) — it is modest, as it were, in its first motions and proposals, but having once got footing in the heart by them, it constantly makes good its ground, and presseth on to some farther degrees in the same kind.
–John Owen (1616-1683), Of The Mortification of Sin in Believers