Gregory of Nyssa

Next he says, "Lightening souls with the light of knowledge." This grace also the doctrine of godliness ascribes alike to the Father, to the Son, and to the Holy Ghost. For He is called a light by David, and from thence the light of knowledge shines in them who are enlightened.

Against Eunomius 2:15 ↗

Augustine of Hippo

Christ's young soldier speaks, on his coming to the faith. "The Lord is my light, and my salvation: whom shall I fear?" [Psalm 27:1]. The Lord will give me both knowledge of Himself, and salvation: who shall take me from Him? "The Lord is the Protector of my life: of whom shall I be afraid?" The Lord will repel all the assaults and snares of mine enemy: of no man shall I be afraid.

Exposition on Psalm 27 ↗

Thomas Aquinas

Having presented the prayer, the Psalmist here consequently speaks of the confidence conceived from prayer. And concerning this he does two things. First, he presents the confidence conceived. Second, he prays again that he not fail in his confidence, at "To you, O Lord." The title: "Unto the end, a Psalm before he was anointed." It should be noted that, as the Gloss explains at greater length, David was anointed king three times. First by Samuel, 1 Sam. 16. And then he was not yet king, but had the sign of kingship. …

Exposition on the Psalms of David ↗

Bonaventure

Scripture enlightens in a circle, as, for instance, when it advises us not to flee, because we have protection all around. For we have the Lord and angels about us, wherefore the Psalm: Mountains are round about Jerusalem; so the Lord is round about His people. To the servant of Eliseus who cried out because of the Syrian robbers who sought to capture him, Eliseus said: "Lord, open his eyes, that he may see." And the Lord opened the eyes of the servant, and he saw. …

Collations on the Hexaemeron, Collation 17 ↗