To his complaint in the preceding verse he now subjoins an imprecation, that God would cut off deceitful tongues. It is uncertain whether he wishes that deceitful men may be utterly destroyed, or only that the means of doing mischief may be taken from them; but the scope of the passage leads us rather to adopt the first sense, and to view David as desiring that God, by some means or other, would remove that plague out of the way. As he makes no mention of malice, while he inveighs so vehemently against their envenomed tongues, we hence conclude, that he had suffered much more injury from the latter than from the former; and certainly falsehood and calumnies are more deadly than swords and all other kind of weapons. From the second clause of the third verse it appears more clearly what kind of flatterers they were of whom mention was made in the preceding verse: The tongue that speaketh great or proud things. Some flatter in a slavish and fulsome manner, declaring that they are ready to do and suffer any thing which they possibly can for our benefit. But David here speaks of another kind of flatterers, namely, those who in flattering proudly boast of what they will accomplish, and mingle base effrontery and threatening with their deceitful arts. He does not, therefore, speak of the herd of mean conceited persons among the common people who make a trade of flattering, that they may live at other people's expense; but he points his imprecation against the great calumniators of the court to which he was attached, [1] who not only insinuated themselves by gentle arts, but also lied designedly in boasting of themselves, and in the big and haughty discourse with which they overwhelmed the poor and simple. This the Psalmist confirms more fully in the following verse: Who have said, we will be strengthened by our tongues Those must be possessed of great authority who think that, in the very falsehood to which they are addicted, they have enough of strength to accomplish their purposes, and to protect themselves. It is the utmost height of wickedness for persons to break out into such presumption, that they scruple not to overthrow all law and equity by their arrogant and boasting language; for, in doing this, it is just as if they openly declared war against God himself. Some read, we will strengthen our tongues. This reading is passable, in so far as the sense is concerned, but it scarcely agrees with the rules of grammar, because the letter l, lamed, is added. Moreover, the sense which is more suitable is this: that the wicked persons spoken of being armed with their tongues, go beyond all bounds, and think they can accomplish by this means whatever they please; just as this set of men so deform every thing with their calumnies, that they would almost cover the sun himself with darkness.

Footnotes

1 - "The occasion on which this psalm was composed is not expressed, but it is a sad complaint of the corrupt manners of that age, (especially of the court of Saul, 5:3,) in which it was hard to find an honest plain dealing man, in whom one might confide. Some think it aims partly at Doeg, and such like courtiers; partly at the Ziphires, and such perfidious people in the country, who, promising him their friendship, (as Theodoret understands it,) would have most basely betrayed him unto Saul, his declared enemy." -- Bishop Patrick's Paraphrase on the Book of Psalms.

The Lord shall cut off - This might be rendered, "May the Lord cut off," implying a wish on the part of the psalmist that it might occur. But probably the common rendering is the correct one. It is the statement of a solemn truth, designed for warning, that all such persons would be punished.
All flattering lips - The meaning is, that he will cut off all "persons" who use flattery; that is, he will cut them off from the favors which he will show to his own people, or will punish them. The word used here is the common one to denote disowning or excommunicating, and derives its meaning from the act of separating offenders from a community. See Genesis 17:14; Leviticus 17:10; Leviticus 18:29; Leviticus 20:3, Leviticus 20:6; et soepe.
And the tongue that speaketh proud things - That boasts, or is self-confident. For an example of this, see Isaiah 28:15; and compare the notes at that passage. It was this disposition to falsehood, flattery, and boasting, which constituted the fact stated in Psalm 12:1, that "godly" and "faithful" men - men on whom reliance might be placed, whose word might be trusted, and whose promised aid in the cause of truth might be depended on - had seemed to "fail" among men. That is, no such men could be found.

Proud things - גדלות gedoloth, great things; great swelling words, both in their promises and in their commendations.

The Lord shall cut off all flattering lips,.... This is either a prophecy or a prayer, as Aben Ezra and Kimchi observe; that God either would or should cut off such who used flattery with their lips, by inflicting some judgment in this life, or everlasting punishment hereafter; by taking them away by death "out of the world", as the Targum paraphrases it; or by casting them into hell, where all liars and deceitful persons will have their portion; see Job 32:21;
and the tongue that speaketh proud things, or "great things" (f), as the little horn, Daniel 7:20; and the beast, or Romish antichrist, who is designed by both, Revelation 13:5; and which will be accomplished when Christ shall destroy him with the breath of his mouth, and the brightness of his coming; and indeed every tongue that riseth up against God, Christ, and his people, will be condemned; when ungodly sinners will be convinced of all their hard speeches, Isaiah 54:17, Jde 1:15. Perhaps some regard may be had to the tongue of Doeg the Edomite; see Psalm 52:3.
(f) "magna", Pagninus, Montanus, Vatablus, Piscator, Gejerus, Michaelis; "grandia", Cocceius.

Boasting (Daniel 7:25) is, like flattery, a species of lying.
lips, and . . . tongue--for persons.

(Hebrews.: 12:4-5) In this instance the voluntative has its own proper signification: may He root out (cf. Psalm 109:15, and the oppositive Psalm 11:6). Flattering lips and a vaunting tongue are one, insofar as the braggart becomes a flatterer when it serves his own selfish interest. אשׁר refers to lips and tongue, which are put for their possessors. The Hiph. הגבּיר may mean either to impart strength, or to give proof of strength. The combination with ל, not בּ, favours the former: we will give emphasis to our tongue (this is their self-confident declaration). Hupfeld renders it, contrary to the meaning of the Hiph.: over our tongue we have power, and Ewald and Olshausen, on the ground of an erroneous interpretation of Daniel 9:27, render: we make or have a firm covenant with our tongue. They describe their lips as being their confederates (את as in 2-Kings 9:32), and by the expression "who is lord over us" they declare themselves to be absolutely free, and exalted above all authority. If any authority were to assert itself over them, their mouth would put it down and their tongue would thrash it into submission. But Jahve, whom this making of themselves into gods challenges, will not always suffer His own people to be thus enslaved.