If he sees this serpent creeping into his bosom

(Thomas Watson, "The Upright Man's Character")

"How then can I do this great wickedness, and sin
 against God?" Genesis 39:9

A godly man will not allow himself in any known sin.
He dares not touch the forbidden fruit.

Every man but has a propensity and inclination to
a certain sin. This one master-sin is as dear to him
as his right eye! This sin is Satan's citadel, all his
strength lies here. The devil can hold a man as fast
by this one link, as by a whole chain of vices. The
fowler has the bird held fast enough by one wing.
Herod did many things, but there was one sin so
dear to him, that he would sooner behead the
prophet, than behead that sin!

A godly man will not indulge himself in this darling sin.
He takes the sacrificing knife of mortification—and runs
it through his dearest sin! "I was also upright before
Him, and kept myself from my iniquity." Psalm 18:23

An upright heart is not only angry with sin, but hates sin!
If he sees this serpent creeping into his bosom, the
nearer it is, the more he hates it!