As he furthers his discussion of what mortification is, Owen goes on to say in Chapter 6 that if we are fight our enemy (sin), then it would do us well to understand our enemy fully. And that is the analogy he draws out here. Do we ponder the enemy, or do we just fight it ignorantly. This is powerful paragraph:
To labor to be acquainted with the ways, wiles, methods, advantages, and occasions of its success is the beginning of this warfare. So do men deal with enemies. They inquire out their counsels and designs, ponder their ends, consider how and by what means they have formerly prevailed, that they may be prevented. In this consists the greatest skill in conduct. Take this away, and all waging of war, wherein is the greatest improvement of human wisdom and industry, would be brutish. So do they deal with lust who mortify it indeed. Not only when it is actually vexing, enticing, and seducing, but in their retirements13 they consider, “This is our enemy; this is his way and progress, these are his advantages, thus has he prevailed, and thus he will do, if not prevented.” So David, “My sin is ever before me” (Ps. 51:3). And, indeed, one of the choicest and most eminent parts of practically spiritual wisdom consists in finding out the subtleties, policies, and depths of any indwelling sin; to consider and know wherein its greatest strength lies—what advantage it uses to make of occasions, opportunities, temptations—what are its pleas, pretenses, reasonings—what its stratagems, colors,14 excuses; to set the wisdom of the Spirit against the craft of the old man; to trace this serpent in all its turnings and windings; to be able to say, at its most secret and (to a common frame of heart) imperceptible actings, “This is your old way and course; I know what you aim at”—and so to be always in readiness is a good part of our warfare.