Albert Barnes Commentary Psalms 12:3

"Jehovah will cut off all flattering lips, The tongue that speaketh great things;" — Psalms 12:3 (ASV)

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, 6; and frequently elsewhere).

And the tongue that speaks 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 (Psalms 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.