See here, 1. What an abominable thing sin is, and how hateful sometimes it is made to appear, even to the sinner himself. When his conscience is convinced, or he feels smart from his sin, he is sick of it, and vomits it up; he seems then to detest it and to be willing to part with it. It is in itself, and, first or last, will be to the sinner, more loathsome than the vomit of a dog, Psa 36:2. 2. How apt sinners are to relapse into it notwithstanding. As the dog, after he has gained ease by vomiting that which burdened his stomach, yet goes and licks it up again, so sinners, who have been convinced only and not converted, return to sin again, forgetting how sick it made them. The apostle (Pe2 2:22) applies this proverb to those that have known the way of righteousness but are turned from it; but God will spue them out of his mouth, Rev 3:16.

As a dog returneth to his vomit,.... Who being sick with what he has eaten, casts it up again, and afterwards returns unto it and licks it up;

so a fool returneth to his folly, or "repeats" (a) it, time after time, many times, as Ben Melech; or a wicked man turns to his wickedness, who, having had some qualms upon his conscience for sin, for a while forsakes it; but that fit being over, and he forgetting all his former horror and uneasiness, returns to his old course of life: a wicked man is here compared to a dog, as he is elsewhere for his impudence and voraciousness in sinning; and the filthiness of sin is expressed by the vomit of a dog, than which nothing is more nauseous and loathsome; and the apostasy of the sinner, from an external course of righteousness into open profaneness is signified by the return of this creature to it. This is said to be a "true proverb", Pe2 2:22, where it is quoted and applied.

(a) "qui iterat", Tigurine version, Michaelis; "iterans", Montanus, Mercerus, Cocceius, Gejerus; "duplicans", Schultens.

returneth . . . folly--Though disgusting to others, the fool delights in his folly.