18 In praises of God, in confessions of sins, in hymns and in songs, in prayers, “There is a multitude of the sound of waters. The clouds have uttered a voice”. Thence that sound of waters, thence the troubling of the abysses, because “the clouds have uttered a voice.” What clouds? The preachers of the word of truth. What clouds? Those concerning which God does menace a certain vineyard, which instead of grape had brought forth thorns and He says, “I will command My clouds, that they rain no rain upon it.” In a word, the Apostles forsaking the Jews, went to the Gentiles: in preaching Christ among all nations, “the clouds have uttered a voice.”
“For Your arrows have gone through.” Those same voices of the clouds He has again called arrows. For the words of the Evangelists were arrows. For these things are allegories. For properly neither an arrow is rain, nor rain is an arrow: but yet the word of God is both an arrow because it does smite; and rain because it does water. Let no one therefore any longer wonder at the troubling of the abysses, when “Your arrows have gone through.” What is, “have gone through”? They have not stopped in the ears, but they have pierced the heart.
“The voice of Your thunder is in the wheel”. What is this? How are we to understand it? May the Lord give aid. When boys we were wont to imagine, whenever we heard thunderings from Heaven, that carriages were going forth as it were from the stables. For thunder does make a sort of rolling like carriages. Must we return to these boyish thoughts, in order to understand, “the voice of Your thunder is in the wheel,” as though God has certain carriages in the clouds, and the passing along of the carriages does raise that sound?
Far be it. This is boyish, vain, trifling. What is then, “The voice of Your thunder is in the wheel”? Your voice rolls. Not even this do I understand. What shall we do? Let us question Idithun himself, to see whether perchance he may himself explain what he has said: “The voice,” he says, “of Your thunder is in the wheel.” I do not understand. I will hear what you say, “Your lightnings have appeared to the round world.” Say then, I had no understanding. The round world is a wheel. For the circuit of the round world is with reason called also an “orb:” whence also a small wheel is called an “orbiculus.”
“The voice of Your thunder is in the wheel:” Your “lightnings have appeared to the round world.” Those clouds in a wheel have gone about the round world, have gone about with thundering and with lightning, they have shaken the abyss, with commandments they have thundered, with miracles they have lightened. “Unto every land has gone forth the sound of them, and unto the ends of the orb the words of them.” “The land has been moved and made to tremble:” that is, all men that dwell in the land.
But by a figure the land itself is sea. Why? Because all nations are called by the name of sea, inasmuch as human life is bitter, and exposed to storms and tempests. Moreover if you observe this, how men devour one another like fishes, how the stronger does swallow up the weaker— it is then a sea, unto it the Evangelists went.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)