I say, then, that the first thing in mortification is the weakening of this habit, that it shall not impel and tumultuate as formerly; that it shall not entice and draw aside; that it shall not disquiet and perplex the killing of its life, vigour, promptness, and readiness to be stirring. This is called “crucifying the flesh with the lusts thereof,” Gal. v. 24; that is, taking away its blood and spirits that give it strength and power, — the wasting of the body of death “day by day,” 2 Cor. iv. 16. As a man nailed to the cross; he first struggles, and strives, and cries out with great strength and might, but, as his blood and spirits waste, his strivings are faint and seldom, his cries low and hoarse, scarce to be heard; — when a man first sets on a lust or distemper, to deal with it, it struggles with great violence to break loose; it cries with earnestness and impatience to be satisfied and relieved; but when by mortification the blood and spirits of it are let out, it moves seldom and faintly, cries sparingly, and is scarce heard in the heart; it may have sometimes a dying pang, that makes an appearance of great vigour and strength, but it is quickly over, especially if it be kept from considerable success. This the apostle describes, as in the whole chapter, so especially, Rom. vi. 6.
“Sin,” saith he, “is crucified; it is fastened to the cross.” To what end? “That the body of death may be destroyed,” the power of sin weakened and abolished by little and little, that “henceforth we should not serve sin;” that is, that sin might not incline, impel us with such efficacy as to make us servants to it, as it hath done heretofore. And this is spoken not only with respect to carnal and sensual affections, or desires of worldly things, — not only in respect of the lust of the flesh, the lust of the eyes, and the pride of life, — but also as to the flesh, that is, in the mind and will, in that opposition unto God which is in us by nature. Of what nature soever the troubling distemper be, by what ways soever it make itself out, either by impelling to evil or hindering from that which is good, the rule is the same; and unless this be done effectually, all after-contention will not compass the end aimed at. A man may beat down the bitter fruit from an evil tree until he is weary; whilst the root abides in strength and vigour, the beating down of the present fruit will not hinder it from bringing forth more. This is the folly of some men; they set themselves with all earnestness and diligence against the appearing eruption of lust, but, leaving the principle and root untouched, perhaps unsearched out, they make but little or no progress in this work of mortification.
John Owen, The Mortification of Sin