“Now, it being our duty to mortify, to be killing of sin whilst it is in us, we must be at work. He that is appointed to kill an enemy, if he leave striking before the other ceases living, doth but half his work, Gal. 6:9; Heb. 12:1; 2 Cor. 7:1.
Sin doth not only still abide in us, but is still acting, still labouring to bring forth the deeds of the flesh. When sin lets us alone we may let sin alone; but as sin is never less quiet than when it seems to be most quiet, and its waters are for the most part deep when they are still, so ought our contrivances against it to be vigorous at all times and in all conditions, even where there is least suspicion.”
– John Owen –
Works, volume 6, page 11