Emphasis is laid (see the Proverbs 2:16 note) upon the origin of the beguiler.

And why wilt thou, my son, be ravished with a strange woman,.... Or "err with her" (y); after all those inconveniences and miseries that follow upon a conversation with a harlot, and all those advantages of a marriage state set before thee; why wilt thou be, so foolish and mad as to have a fondness for an harlot and dote upon her, and neglect entering into a marriage state, or forsake the wife of youth? and yet though things are so clearly stated and aptly represented, and the expostulation made in the most tender and affectionate manner; it is suggested as if after all it would not be attended unto, but a harlot be preferred to a wife of youth, a filthy beast to a loving hind, and dirty puddles of water in a ditch to running streams from a well or fountain;
and embrace the bosom of a stranger? that is not thy wife; a description of unlawful love and impure embraces, which are dissuaded from.
(y) "Errares", Junius & Tremellius, Piscator; "aberrares", Cocceius.

The answer to the Why? in this verse is: no reasonable cause - only beastly sensuality, only flagitious blindness can mislead thee. The ב of בזרה is, as 19b and Isaiah 28:7, that of the object through which one is betrayed into intoxication. חק (thus, according to the Masora, four times in the O.T. for חיק) properly means an incision or deepening, as Arab. hujr (from hjr, cohibere), the front of the body, the part between the arms or the female breasts, thus the bosom, Isaiah 40:11 (with the swelling part of the clothing, sinus vestis, which the Arabs call jayb), and the lap; חבּק (as Proverbs 4:8), to embrace, corresponds here more closely with the former of these meanings; also elsewhere the wife of any one is called אשת חיקו or השׁכבת בחיקו, as she who rests on his breast. The ancients, also J. H. Michaelis, interpret Proverbs 5:15-20 allegorically, but without thereby removing sensual traces from the elevated N.T. consciousness of pollution, striving against all that is fleshly; for the castum cum Sapientia conjugium would still be always represented under the figure of husband and wife dwelling together. Besides, though זרה might be, as the contrast of חכמה, the personified lust of the world and of the flesh, yet 19a is certainly not the חכמה, but a woman composed of flesh and blood. Thus the poet means the married life, not in a figurative sense, but in its reality - he designedly describes it thus attractively and purely, because it bears in itself the preservative against promiscuous fleshly lust.