3 “He has talked vanity each man to his neighbour”. By neighbour we must understand every man: for that there is no one with whom we should work evil; “and the love of our neighbour works no evil.” “Deceitful lips, with a heart and a heart they have spoken evil things.” The repetition, “with a heart and a heart,” signifies a double heart.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)