Thomas Aquinas, on Ps 17:33

“God who hath girt me with strength; and made my way blameless.”

“"Who." Here agility is set forth, which is necessary for fighting. 1 Sam. 24 says that Saul went out against David over the most precipitous rocks, which are passable only by deer; as if to say: God conferred such agility upon me that I went like a deer over the mountains. "And upon the heights he has set me." On steep mountains human footsteps are not firmly planted, but God gave him such grace that he did not slip on them. Mystically it is read thus: a deer crosses thorns and forests without injury; so the spiritual affection passes through without injury and infection from evil things and the pleasures of the world: Gen. 49: "Naphtali is a deer let loose, giving beautiful words." Is. 35: "Then the lame shall leap like a deer." "And upon the heights he has set me," that is, he has fixed my mind upon heavenly things: Hab. 3: "Upon my high places the conqueror will lead me." Next military training is set forth; hence he says, "who teaches my hands for battle." Military training is acquired through knowledge and perfected through exercise. First, therefore, he seeks knowledge or training, because this training is necessary for soldiers. Prov. 24: "War is begun with planning." But this one, taught by God, says regarding the second, "you have made my arms like a bow of bronze," that is, you have given me arms that are, as it were, indefatigable for fighting. Or "who teaches," etc., that is, against vices and demons, he teaches us to work to overcome enemies who try to close the gates of heaven. Then, changing the person, he says, "you have made," etc. Another reading has, "you have broken the bow of bronze," that is, my arm. Ps. 143: "Blessed be the Lord my God, who teaches my hands to fight," etc. Note that the excellence of agility and the excellence of strength are found in lions, which from excessive dryness have no marrow in their bones; and these things occur from a great inequality of the mixed elements, and therefore they live a short time; and this is not fitting in a person on account of his activities. Hence such things are said to have been given to David as a special gift, as is said in Sir. 47: "He played with lions as with lambs, and with bears he did likewise as with their lambs." And similarly, the skill of fighting was given to him by God through grace, mystically. We must be trained in spiritual warfare. Sir. 11: "Many are the snares of the deceitful," which we cannot escape unless we have both training and divine help. Job 39: "The glory of his nostrils," that is, the demon's, "is terror; he despises fear and does not yield to the sword." 2 Cor. 4: "Although he who is our outward man is corrupted, yet he who is the inward man is renewed day by day."”

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