Clement of Rome

This is the way, dear friends, in which we found out salvation, namely Jesus Christ, the high priest of our offerings, the guardian and helper of our weakness. Through him let us look steadily into the heights of heaven; through him we see as in a mirror his faultless and transcendent face; through him the eyes of our hearts have been opened; through him our foolish and darkened mind springs up into the light; through him the Master has willed that we should taste immortal knowledge, for "he, being the radiance of his majesty, is as …

1 Clement 36 ↗

Augustine of Hippo

"Who makes spirits His angels, and flaming fire His ministers" [Psalm 104:4]: that is, those who are already spirits, who are spiritual, not carnal, He makes His Angels, by sending them to preach His gospel. "And flaming fire His ministers." For unless the minister that preaches be on fire, he enflames not him to whom he preaches.

Exposition on Psalm 104 ↗

Jerome

You who make your angels spirits. What he passed over in Genesis, he indicated in this verse. For although God created all things, he made no mention anywhere of the angels. And he said, You who make your angels spirits, for this reason: because the angels do not have a body, but are wholly light. And your ministers a burning fire. He signifies their purity, and that they are not subject to sins. In another sense: for example, someone is holy, and a good angel, an angel of light, is sent to him. …

Homily 30, on Psalm 103 ↗

Gregory the Dialogist

It should also be known that the word "angel" is a name of office, not of nature. For those holy spirits of the heavenly homeland are indeed always spirits, but they cannot always be called angels, since they are angels only when something is announced through them; hence it is said through the Psalmist: "Who makes His angels spirits." As if he were saying plainly: He who always has them as spirits also makes them angels when He wills. …

Forty Gospel Homilies, Homily 34 ↗