Charles H. Spurgeon on Psalms 18:23

Growth in mortification. . . . Men may deceive themselves when they estimate their progress herein by having overcome such lusts as their natures are not so prone unto. The surest way is to take a judgment of it from the decay of a man's bosom-sin, even as David did estimate his uprightness by his "keeping himself from his iniquity;" so a man of his growth in uprightness. When physicians would judge of a consumption of the whole, they do it not by the falling away of any part whatever, as of the flesh in the face alone, or any the like; such a particular abatement of flesh in some one part may come from some other cause; but they use to judge by the falling away of the brawn of the hands, or arms and thighs, etc., for these are the more solid parts. The like judgments do physicians make upon other diseases, and of the abatement of them from the decrease in such symptoms as are pathognomical, and proper, and peculiar to them. In like manner also the estimate of the progress of the victories of a conqueror in an enemy's kingdom is not taken from the taking or burning of a few villages or dorps, but by taking the forts and strongest holds, and by what ground he hath won upon the chief strength, and by what forces he hath cut off of the main army. Do the like in the decrease of, and victory over, your lusts. —Thomas Goodwin.