Augustine of Hippo

Take care not to let trust in your own strength steal on you, for you are human, and "cursed be everyone who puts his hope in man." But put your trust fully and with your whole heart in God, and he will be your strength; trust him lovingly and gratefully and say to him humbly and faithfully, "I will love you, O Lord, my strength," because that very charity of God, when it is perfected in us, "casts out fear."

Letter 218 ↗

Thomas Aquinas

In the preceding Psalm the Psalmist prayed to be delivered from his enemies; here, having been delivered, he gives thanks. And first he gives thanks for the benefit of deliverance. Second, he breaks forth into praise of the deliverer, at "the heavens declare the glory of God." The title: "Unto the end, for the servant of the Lord, David. And he spoke the words of this canticle on the day the Lord delivered him from the hand of all his enemies and from the hand of Saul." And this Psalm is found word for word in 2 Sam. 22. …

Exposition on the Psalms of David ↗

Bonaventure

"I will love you, O Lord, my fortitude; the Lord is my firmament and my refuge and my deliverer." Catherine and Lucy were strong through the love of God. If we are not bound to the Lord through charity, we easily lose our fortitude.

Collationes de Septem Donis, Collation 5 ↗