3 “Who makes spirits His angels, and flaming fire His ministers”: 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.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)