John Calvin 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)

Every man speaks deceit. David in this verse describes that part of unrighteousness which is contrary to truth. He says that there is no sincerity or uprightness in their speech, because their primary goal is to deceive.

He next describes the manner in which they deceive: namely, that every man tries to ensnare his neighbor by flattery. He also points out the source and root cause of this: They speak with a double heart.

This doubleness of heart, so to speak, makes people double and variable in their speech, in order to disguise themselves in different ways, or to make themselves appear to others different from what they really are. Thus the Hebrew word חלקות, chalakoth, which means flattery, is derived from a word which means division.

Just as those who are resolved to act truthfully in their interactions with their neighbors freely and ingenuously lay open their whole heart, so treacherous and deceitful persons keep a part of their feelings hidden within their own hearts, and cover it with the veneer of hypocrisy and a pleasant exterior, so that from their speech we cannot discern anything certain about their intentions. Our speech, therefore, must be sincere so that it can be, as it were, a mirror in which the uprightness of our heart can be seen.