I've been struck by the violent imagery of mortification. You cannot talk about putting sins to death without talking about death and killing, which is heavy. John Owen, like Saint Paul, not only uses the analogy of putting our sin to death, but even the specific analogy of crucifixion.
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 vigor 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. 6:6.
John Owen, The Mortification of Sin, Chapter 6
Thus we can expect sin to resist mightily at first in the same way as a desperate animal fighting for its life. The violence of mortification turns my stomach with discomfort, but I believe this is one of the only situations where the violence is justified and necessary. Sin is working craftily always against God and toward our complete destruction, and it will never stop. Either we will kill it, or it will kill us.