When a man hath thus for a season been deluded, and hath deceived his own soul, and finds in a long course of life that indeed his sin is not mortified, or if he hath changed one he hath gotten another, he begins at length to think that all contending is in vain, —he shall never be able to prevail; he is making a dam against water that increaseth on him. Hereupon he gives over, as one despairing of any success, and yields up himself to the power of sin and that habit of formality that he hath gotten.
And this is the usual issue with persons attempting the mortification of sin without an interest in Christ first obtained. It deludes them, hardens them,—destroys them. And therefore we see that there are not usually more vile and desperate sinners in the world than such as, having by conviction been put on this course, have found it fruitless, and deserted it without a discovery of Christ. And this is the substance of the religion and godliness of the choicest formalists in the world, and of all those who in the Roman synagogue are drawn to mortification, as they drive Indians to baptism or cattle to water. I say, then, that mortification is the work of believers, and believers only. To kill sin is the work of living men; where men are dead (as all unbelievers, the best of them, are dead), sin is alive, and will live.
– John Owen –
from The Mortification of Sin in Believers, volume 6 of Works, page 37