Augustine of Hippo

"His truth shall surround thee with a shield." What are "the wings," the same is "the shield:" since there are neither wings nor shield. If either were literally, how could the one be the same as the other? can wings be a shield or a shield wings? But all these expressions, indeed, are figuratively used through likenesses. …

Exposition on Psalm 91 ↗

Jerome

You shall not fear from the terror of the night. The just man has no terror of the night, but of the day. "Come, children, hear me, I will teach you the fear of the Lord." Those who are the children of the prophets have no terror of the night, nor of the darkness, but of the light and of the day. "That they may shoot in secret at the upright of heart." The devil does not send his arrows in the day, lest he be seen. For everything that is done in the light is made manifest by the light.

Homily 68, on Psalm 90 (Alternate Series) ↗

Bonaventure

The third part of the perfection of the fear of the Lord consists in the perfect firmness of confidence: because the fear of the Lord is a tower of firmness and confidence, because it renders a person secure from every other fear. "His truth shall encompass you with a shield; you shall not fear the terror of the night, nor the arrow that flies by day, nor the pestilence that walks in darkness, nor the assault and the noonday devil." He who does not fear God must fear everywhere; and he who truly fears God has what no one can take …

Collationes de Septem Donis, Collation 2 ↗