From Owen's Of the Mortification of Sin in Believers...
Of the Mortification of Sin in Believers:
What Mortification of Sin is Not
From Chapter 5:
(2.) I think I need not say it is not the dissimulation of a sin. When a man on some outward respects forsakes the practice of any sin, men perhaps may look on him as a changed man. God knows that to his former iniquity he hath added cursed hypocrisy, and is got in a safer path to hell than he was in before. He hath got another heart than he had, that is more cunning; not a new heart, that is more holy.
(3.) The mortification of sin consists not in the improvement of a quiet, sedate nature. Some men have an advantage by their natural constitution so far as that they are not exposed to such violence of unruly passions and tumultuous affections as many others are. Let now these men cultivate and improve their natural frame and temper by discipline, consideration, and prudence, and they may seem to themselves and others very mortified men, when, perhaps, their hearts are a standing sink of all abominations. Some man is never so much troubled all his life, perhaps, with anger and passion, nor doth trouble others, as another is almost every day; and yet the latter hath done more to the mortification of the sin than the former. Let not such persons try their mortification by such things as their natural temper gives no life or vigour to. Let them bring themselves to self-denial, unbelief, envy, or some such spiritual sin, and they will have a better view of themselves.
(4.) A sin is not mortified when it is only diverted. Simon Magus for a season left his sorceries; but his covetousness and ambition, that set him on work, remained still, and would have been acting another way. Therefore Peter tells him, “I perceive thou art in the gall of bitterness;” — “Notwithstanding the profession thou hast made, notwithstanding thy relinquishment of thy sorceries, thy lust is as powerful as ever in thee; the same lust, only the streams of it are diverted. It now exerts and puts forth itself another way, but it is the old gall of bitterness still.” A man may be sensible of a lust, set himself against the eruptions of it, take care that it shall not break forth as it has done, but in the meantime suffer the same corrupted habit to vent itself some other way; as he who heals and skins a running sore thinks himself cured, but in the meantime his flesh festereth by the corruption of the same humour, and breaks out in another place. And this diversion, with the alterations that attend it, often befalls men on accounts wholly foreign unto grace: change of the course of life that a man was in, of relations, interests, designs, may effect it; yea, the very alterations in men’s constitutions, occasioned by a natural progress in the course of their lives, may produce such changes as these. Men in age do not usually persist in the pursuit of youthful lusts, although they have never mortified any one of them. And the same is the case of bartering of lusts, and leaving to serve one that a man may serve another. He that changes pride for worldliness, sensuality for Pharisaism, vanity in himself to the contempt of others, let him not think that he hath mortified the sin that he seems to have left. He hath changed his master, but is a servant still.