The words of the wicked are to lie in wait—a lying in wait—for blood (see Proverbs 1:11). The wicked, by their lies, slanders, false accusations, etc; endanger men's lives, as Jezebel compassed Naboth's death by false witness (1 Kings 21:13).
The mouth of the upright shall deliver them; i.e. the innocent whose blood the wicked seek. The good plead the cause of the oppressed, using their eloquence in their favour, as in the Apocryphal Story of Susannah, Daniel saved the accused woman from the slanders of the elders.