Every man speaketh deceit. David in this verse sets forth that part of unrighteousness which is contrary to truth. He says that there is no sincerity or uprightness in their speech, because the great object upon which they are bent is to deceive. He next describes the manner in which they deceive, namely, that every man endeavors to ensnare his neighbor by flattery [1] He also points out the fountain and first cause of this, They speak with a double heart. This doubleness of heart, as I may term it, makes men double and variable in their speech, in order thereby to disguise themselves in different ways, or to make themselves appear to others different from what they really are. Hence the Hebrew word chlqvt, chalakoth, which denotes flattery, is derived from a word which signifies division. As those who are resolved to act truthfully in their intercourse with their neighbors, freely and ingenuously lay open their whole heart; so treacherous and deceitful persons keep a part of their feeling hidden within their own breasts, and cover it with the varnish of hypocrisy and a fair outside; so that from their speech we cannot gather any thing certain with respect to their intentions. Our speech, therefore, must be sincere in order that it may be as it were a mirror, in which the uprightness of our heart may be beheld.

Footnotes

1 - Horsley reads "smooth lips." "Not smooth," says he, "with flattery, but with glossing lies, with ensnaring eloquence and specious arguments in support of the wretched cause which they espouse."

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 of the ways was that there was a disregard of truth; that no confidence could be placed on the statements of those who professed to be pious; that 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 neighbour - 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 - means properly to divide, to distribute; then, to make things equal or smooth; then, to make smooth or to shape, as an artisan does, as with a plane; and then, "to make things smooth with the tongue," that is, "to flatter." See Psalm 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; none that they were not intended to deceive. Flattery is the ascribing of qualities to another which 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 gives utterance to the words, and the other that retains 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 give utterance to the words which he uses toward his neighbor, and another that conceals his real purpose or design. No confidence, therefore, could be placed in such persons. Compare the note at Job 32:22.

They speak vanity every one with his neighbor - They are false and hollow; they say one thing while they mean another; there is no trusting to what they say.
Flattering lips, and with a double heart do they speak - בלב ולב beleb valeb, "With a heart and a heart." They seem to have two hearts; one to speak fair words, and the other to invent mischief. The old MS. both translates and paraphrases curiously.
Trans. Dayn spak ilkan til his neghbur: swykil lippis in hert, and thurgh hert thai spak.
Par - Sothfastnes es lessed, and falsed waxes: and al sa vayn spak ilkone to bygyle his neghbur: and many spendes thair tyme in vayne speche withoutyn profyte and gastely frute. And that er swyku lippis; that er jangelers berkand ogaynes sothfastnes. And swykel, for thai speke in hert and thurgh hert; that es in dubil hert, qwen a fals man thynkes ane, and sais another, to desaif hym that he spekes with.
This homely comment cannot be mended.

They speak vanity every one with his neighbour: [with] (b) flattering lips [and] with a double heart do they speak.
(b) He means the flatters of the court which hurt him more with their tongues than with their weapons.

They speak vanity everyone with his neighbour,.... That which is false and a lie, either doctrinal or practical; what was not according to the word of God, and was vain and empty, frothy, filthy, and corrupt; and which no godly and faithful man would do. And this being done in common, by the generality of men, one with another, shows the degeneracy of the age, and supports the complaint before made. They speak even
with flattering lips; as Cain did to Abel, Joab to Amasa, the Herodians to Christ, Judas to his Master, false teachers to those that are simple, hypocrites to God himself, when they draw nigh to him only with their lips, and all formal professors to the churches of Christ, when they profess themselves to be what they are not. And this is a further proof of the justness of the above complaint;
and with a double heart do they speak: or "with an heart and an heart" (d); such are double minded men, who say one thing, and mean another; their words are not to be depended upon; there is no faithfulness in them. The Chinese (e) reckon a man of "two hearts", as they call him, a very wicked man, and none more remote from honesty.
(d) "in corde & corde", V. L. Pagninus, Montanus, Gejerus. (e) Martin. Sinic. Hist. p. 144. a heart having , a double meaning, as Pittacus says, Laert. in Vit. Pittac. l. 1. p. 53.

The want of it is illustrated by the prevalence of deceit and instability.