They speak vanity— They speak falsehood. Mudge. A double heart, in the Hebrew is ולב בלב beleb valeb, with heart and heart; that is, they spake as if they had two hearts: the one to hate their neighbour and form designs against him, and the other to prompt the tongue to pretend a friendship for him.
Related Commentaries of Psalms 12:2
Psalms 12:2
2 They speak vanity every one with his neighbour: with flattering lips and with a doublea heart do they speak.