12 “The head of their going about, the toil of their own lips shall cover them”. Me, he says, the shadow of Your wings shall cover: for, “You have covered me in the day of battle.” Them what shall cover? “The head of their going about;” that is, pride. What is, “their going about”? How they go about and stand not, how they go in the circle of error, where is journeying without end. He who goes in a straight line, begins from some point, ends at some point: he who goes in a circle, never ends. That is the toil of the wicked, which is set forth yet more plainly in another Psalm, “The wicked walk in a circle.” But “the head of their going about” is pride, for pride is the beginning of every sin. But whence is pride “the toil of their own lips”? Every proud man is false, and every false man is a liar. Men toil in speaking falsehood; for truth they could speak with entire facility. For he toils, who makes what he says: he who wishes to speak the truth, toils not, for truth herself speaks without toil....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)