Thomas Aquinas, on Ps 16:13

“Arise, O Lord, disappoint him and supplant him; deliver my soul from the wicked one: thy sword”

“"Arise." Here he sets forth the other petition, that is, the overthrow of the enemies. And he sets forth three things. First, the petition. Second, the explanation, at "Rescue my soul." Third, the reason for the petition, at "From your hidden ones." Concerning the first, he does two things. First, he addresses the concealment of help. Second, for the destruction of the adversary. He says, therefore: You seem to sleep while you allow me to be afflicted; but "Arise, O Lord, forestall him," so that you may come to my aid more quickly than he can harm me. "And trip him up," that is, undermine him, as it were, by cunning: Job 5: "He catches the wise in their own craftiness." Prov. 19: "A man's cunning trips up his steps." "Trip him up" in two things: namely, in my deliverance; and regarding this he says, "Rescue my soul from the wicked one," who persecutes me against justice, and therefore is wicked. Ps. 42: "Rescue me from the unjust and deceitful man." And the reason for this is that my soul is a sword, that is, a sharp blade on both sides, by which the Devil was destroyed. And this is properly said of the soul of Christ: Is. 27: "On that day the Lord will visit Leviathan with his hard and strong sword."”

Imported from an open dataset — not yet checked against the printed edition.