Fair speech - The Hebrew word is usually translated "doctrine," or "learning" Proverbs 1:5; Proverbs 4:2; Proverbs 9:9; possibly it is used here in keen irony.

With her much fair speech - With her blandishments and lascivious talk, she overcame all his scruples, and constrained him to yield.

With her much fair speech she caused him to yield,.... Or, "to decline" from the right way: or, "inclined him" (d); his ear to listen to her, and his heart to go after her and along with her. This she did, by using a great many words, by her prolixity, and by some taking and striking expressions; lewd women are generally very talkative (e). It may be rendered, "by her much doctrine" (f), as the word is in Proverbs 4:2; so Jezebel calls herself a prophetess, and sets up for a teacher of men; and, by her false doctrine, deceives some that are called the servants of Christ to commit fornication, and eat things sacrificed to idols, Revelation 2:20;
with the flattering of her lips she forced him; to go along with her, not against his will, but with it: though at first there was some reluctance, conscience rose up and opposed; but her words, which were smoother than oil, found a way into his heart, and prevailed upon him to yield to her entreaties; he could no longer withstand her attacks, but surrendered to her; her charming voice, and flattering lips, had more effect upon him than her kisses; notwithstanding these he was reluctant, but could stand it out no longer against her alluring words and soothing language. With this compare the deceivableness of unrighteousness in them that perish through antichrist, 2-Thessalonians 2:10.
(d) "declinare facit eum", Pagninus, Montanus, Vatablus, Gejerus; "flexit", Tigurine version, Junius & Tremellius, Piscator, Mercerus, Michaelin; "inclinavit illum", Cocceius. (e) "Verbosa gaudet Venus Ioquela", Catullus ad Camer. Ep. 53. v. 20. (f) "multitudine discipline suae", Junius & Tremellius, Piscator; "doctrinae suae", Michaelis.

caused . . . yield--or, "inclines."
flattering--(Compare Proverbs 5:3).
forced him--by persuasion overcoming his scruples.

The result: -
21 She beguiled him by the fulness of her talking,
By the smoothness of her lips she drew him away.
Here is a climax. First she brought him to yield, overcoming the resistance of his mind to the last point (cf. 1-Kings 11:3); then drove him, or, as we say, hurried him wholly away, viz., from the right path or conduct (cf. Deuteronomy 13:6, Deuteronomy 13:11). With הטּתּוּ (= הטּתהוּ) as the chief factum, the past imperf. is interchanged, 21b. Regarding לקח, see above, p. 56. Here is the rhetoric of sin (Zckler); and perhaps the לקח of 20a has suggested this antiphrastic לקח to the author (Hitzig), as חלק (the inverted לקח, formed like שׁפל, which is the abstr. of שׁפל as that is of חלק) and תּדּיחנּוּ are reciprocally conditioned, for the idea of the slippery (Psalm 73:18) connects itself with חלק.