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, 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.