But whoso committeth adultery - The case understood is that of a married man: he has a wife; and therefore is not in the circumstances of the poor thief, who stole to appease his hunger, having nothing to eat. In this alone the opposition between the two cases is found: the thief had no food, and he stole some; the married man had a wife, and yet went in to the wife of his neighbor.
Destroyeth his own soul - Sins against his life, for, under the law of Moses, adultery was punished with death; Leviticus 20:10; Deuteronomy 22:22.

But whoso committeth adultery with a woman,.... Which is a greater degree of theft than the former, it being the stealing of another man's wife;
lacketh understanding; or "an heart" (t); the thief lacks bread, and therefore steals, but this man lacks wisdom, and therefore acts so foolish a part; the one does it to satisfy hunger, the other a brutish lust;
he that doeth it destroyeth his own soul; is liable to have his life taken away by the husband of the adulteress; so according to Solon's law (u) the adulterer taken in the act might be killed by the husband: or by the civil magistrate; for according to the law of. Moses he was to die, either to be strangled or stoned; see Gill on John 8:5; and besides, he not only ruins the natural faculties of his soul, besotting, corrupting, and depraving that, giving his heart to a whore, but brings eternal destruction on it; yet so foolish is he, though it issues in the ruin of his precious soul; "he does this" (w), for so the first part of this clause, which stands last in the original text, may be rendered.
(t) "deficit corde", Pagninus, Montanus; "caret corde", Mercerus, Gejerus; so Michaelis. (u) Plutarch. in Vita Solon. p. 90. (w) "ipse faeiet illud", Montanus; "ipse faciet hoc", so some in Vatablus; "is id faciet, sive facit", Cocceius; "ille facit id", Michaelis; "is patrabit illud", Schultens.

lacketh understanding--or, "heart"; destitute of moral principle and prudence.

Here there is a contrast stated to Proverbs 6:30 :
32 He who commits adultery (adulterans mulierem) is beside himself,
A self-destroyer-who does this.
33 He gains stripes and disgrace,
And his reproach is never quenched.
נאף, which primarily seems to mean excedere, to indulge in excess, is, as also in the Decalogue, cf. Leviticus 20:10, transitive: ὁ μοιχεύων γυναῖκα. Regarding being mad (herzlos = heartless) = amens (excors, vecors), vid., Psychologie, p. 254. משׁחית נפשׁו is he who goes to ruin with wilful perversity. A self-murderer - i.e., he intends to ruin his position and his prosperity in life - who does it, viz., this, that he touches the wife of another. It is the worst and most inextinguishable dishonouring of oneself. Singularly Behaji: who annihilates it (his soul), with reference to Deuteronomy 21:12. Eccl. 4:17, where עשׂה would be equivalent to בּטּל, καταργεῖν, which is untrue and impossible.
(Note: Behaji ought rather to have referred to Zephaniah 3:19; Ezekiel 7:27; Ezekiel 22:14; but there עשׂה את means agere cum aliquo, as we say: mit jemandem abrechnen (to settle accounts with any one).)
נגע refers to the corporal punishment inflicted on the adulterer by the husband (Deuteronomy 17:8; Deuteronomy 21:5); Hitzig, who rejects Proverbs 6:32, refers it to the stripes which were given to the thief according to the law, but these would be called מכּה (מכּות). The punctuation נגע־וקלון is to be exchanged for קלונו נגע (Lwenstein and other good editors). מצא has a more active signification than our "finden" (to find): consequitur, τυγχάνει.