Albert Barnes Commentary Psalms 12:2

"They speak falsehood every one with his neighbor: With flattering lip, and with a double heart, do they speak." — Psalms 12:2 (ASV)

They speak vanity - This is a statement of the manner in which the godly and the faithful fail, as stated in Psalm 12:1. One way this occurred was through a disregard for truth: no confidence could be placed in the statements of those who professed to be pious, for they dealt falsely with their neighbors. The word vanity here is equivalent to falsehood. What they spoke was a vain and empty thing, instead of being the truth. It had no reality and could not be depended on.

Every one with his neighbor - In his statements and promises. No reliance could be placed on his word.

With flattering lips - Hebrew, Lips of smoothness. The verb from which the word used here is derived—חלק chālaq—properly means to divide or distribute; then, to make things equal or smooth; then, to make smooth or to shape, as an artisan does, for example with a plane; and then, to make things smooth with the tongue, that is, to flatter (Psalms 5:9; Proverbs 5:3; Proverbs 26:28; Proverbs 28:23; Proverbs 29:5). The meaning is that no confidence could be placed in the statements made. There was no certainty that they were founded on truth, and no assurance that they were not intended to deceive. Flattery is attributing qualities to another that he is known not to possess—usually with some sinister or base design.

And with a double heart - Margin, as in Hebrew, a heart and a heart; that is, as it were, with two hearts: one that utters the words, and the other that holds a different sentiment. Thus, in Deuteronomy 25:13, the phrase in Hebrew, a stone and a stone, means, as it is translated, divers weights—one stone or weight to buy with, and another to sell with. So the flatterer. He has one heart to utter the words that he uses toward his neighbor, and another that conceals his real purpose or design. No confidence, therefore, could be placed in such persons. .