6 “His lightnings gave shine unto the world”. This is great joy. Do we not see? Is it not clear? His lightnings have shined unto the whole world: His enemies have been set on fire, and burnt. All that gainsaid has been burnt, and “His lightnings have given shine unto the world.” How have they shone? That the world might at length believe. Whence were the lightnings? From the clouds. What are the clouds of God? The preachers of the truth. But you see a cloud, misty and dark in the sky, and it has I know not what hidden within it.
If there be lightning from the cloud, a brightness shines forth: from that which you despised, has burst forth that which you may dread. Our Lord Jesus Christ therefore sent His Apostles, as His preachers, like clouds: they were seen as men, and were despised; as clouds appear, and are despised, until what you wonder at gleams from them. For they were in the first place men encumbered with flesh, weak; then, men of low station, unlearned, ignoble: but there was within what could lighten forth; there was in them what could flash abroad.
Peter a fisherman approached, prayed, and the dead arose. His human form was a cloud, the splendour of the miracle was the lightning. So in their words, so in their deeds, when they do things to be wondered at, and utter words to be wondered at, “His lightnings gave shine unto the world; the earth saw it, and was afraid.” Is it not true? Does not the whole Christian world at length exclaim, Amen, afraid at the lightnings which burst forth from those clouds?
Source: The Enarrations, or Expositions, on the Psalms (New Advent)