Psalms 12:2 - Joseph Benson’s Commentary on the Old and New Testaments

They speak vanity Or, falsehood, which is a vain thing, and wants the solidity of truth. With a double heart do they speak See the margin. They speak as if they had two hearts, the one inclining them to hate their neighbour, and form designs against him, and the other to prompt the tongue to pretend a friendship for him. “When men cease to be faithful to their God, he who expects to find them so to each other will be much disappointed. The primitive sincerity will accompany the primitive piety in her flight from the earth; and then interest will succeed conscience in the regulation of human conduct, till one man cannot trust another further than he holds him by that tie.”