You covered it with the deep as with a garment: the waters stood above the mountains.
All Commentaries on Psalms 104:6 Go To Psalms 104
Augustine of Hippo
AD 430
5. "The deep, like a garment, is its clothing" (ver. 6). Whose? Is it perchance God's? But he had already said of His clothing, "Clothed with light as with a garment." I hear of God clothed in light, and that light, if we will, are we. What is, if we will? if we are no longer darkness. Therefore if God is clothed with light, whose clothing, again, is the deep? For an immense mass of waters is called the deep. All water, all the moist nature, and the substance everywhere shed abroad through the seas, and rivers, and hidden caves, is all together called by one name, the Deep. Therefore we understand the earth, of which he said, "He hath founded the earth."Of it I believe he said, "The deep, like a garment is its clothing." For the water is as it were the clothing of the earth, surrounding it and covering it. ...
6. "Above the mountains the waters shall stand:" that is, the clothing of the earth, which is the deep, so increased, that the waters stood even above the mountains. We read of this taking place in the deluge. ...The Prophet minding to foretell future things, not to relate the past, therefore said it, because he would have it understood that the Church should be in a deluge of persecutions. For there was a time when the floods of persecutors had covered God's earth, God's Church, and had so covered it, that not even those great ones appeared, who are the mountains. For when they fled everywhere, how did they but cease to appear? And perchance of those waters is that saying, "Save me, O God, for the waters are come in even unto my soul." Especially the waters which make the sea, stormy, unfruitful. For whatsoever earth the sea-water may have covered, it will not rather make it fruitful than bring it to barrenness. For there were also mountains beneath the waters, because above the mountains waters stood. ...Why were the Apostles hidden by flight? Because "above the mountains the waters stood." The power of the waters was great, but how long? Hear what followeth.