Charles H. Spurgeon on Psalms 18:23

"I was upright." etc. An upright Christian will not allow himself in any known sin; he dares not touch the forbidden fruit. Genesis 39:9. "How then can I do this great wickedness, and sin against God?" Though it be a complexion-sin, he disinherits it. There is no man but doth propend and incline more to one sin than another; as in the body there is one humour predominant, or as in the hive there is one master-bee; so in the heart there is one master-sin; there is one sin which is not only near to a man as the garment, but dear to him as the right eye. This sin is Satan's fort-royal, all his strength lies here; and though we beat down his out-works, gross sin, yet if we let him hold this fort of complexion-sin, it is as much as he desires. The devil can hold a man as fast by this one link, as by a whole chain of vices. The fowler hath the bird fast enough by one wing. Now, an upright Christian will not indulge himself in this complexion-sin: "I was upright before him, and kept myself from mine iniquity." An upright Christian takes the sacrificing knife of mortification, and runs it through his dearest sin. Herod did many things, but there was one sin so dear to him, that he would sooner behead the prophet, than behead that sin. Herod would have a gap for his incest. An upright heart is not only angry with sin (which may admit of reconciliation), but hates sin; and if he sees this serpent creeping into his bosom, the nearer it is the more he hates it. —Thomas Watson.