He hath covered it with the deep as with a garment, This may be understood in two ways, either as implying that now the sea covers the earth as a garment, or that at the beginning, before God by his omnipotent word held gathered the waters together into one place, the earth was covered with the deep. But the more suitable sense appears to be, that the sea is now the covering of the earth. At the first creation the deep was not so much a garment as a grave, inasmuch as nothing bears less resemblance to the adorning of apparel than the state of confused desolation and shapeless chaos in which the earth then was. Accordingly, in my judgment, there is here celebrated that wonderful arrangement by which the deep, although without form, is yet the garment of the earth. But as the context seems to lead to a different view, interpreters are rather inclined to explain the language as denoting, That the earth was covered with the deep before the waters had been collected into a separate place. This difficulty is however easily solved, if the words of the prophet, The waters shall stand above the mountains, are resolved into the potential mood thus, The waters would stand above the mountains; which is sufficiently vindicated from the usage of the Hebrew language. I have indeed no doubt that the prophet, after having said that God had clothed the earth with waters, adds, by way of exposition, that the waters would stand above the mountains, were it not that they flee away at God's rebuke. Whence is it that the mountains are elevated, and that the valleys sink down, but because bounds are set to the waters, that they may not return to overwhelm the earth? The passage then, it is obvious, may very properly be understood thus, -- that the sea, although a mighty deep, which strikes terror by its vastness, is yet as a beautiful garment to the earth. The reason of the metaphor is, because the surface of the earth stands uncovered. The prophet affirms that this does not happen by chance; for, if the providence of God did not restrain the waters, would they not immediately rush forth to overwhelm the whole earth? He, therefore, speaks advisedly when he maintains that the appearance of any part of the earth's surface is not the effect of nature, but is an evident miracle. Were God to give loose reins to the sea, the waters would suddenly cover the mountains. But now, fleeing at God's rebuke, they retire to a different quarter. By the rebuke of God, and the voice of his thunder, is meant the awful command of God, by which he restrains the violent raging of the sea. Although at the beginning, by his word alone, he confined the sea within determinate bounds, and continues to this day to keep it within them, yet if we consider how tumultuously its billows cast up their foam when it is agitated, it is not without reason that the prophet speaks of it, as kept in check by the powerful command of God; just as, both in Jeremiah, (Jeremiah 5:22) and in Job, (Job 28:25) God, with much sublimity, commends his power, as displayed in the ocean. The ascending of the mountains, and the descending of the valleys, are poetical figures, implying, that unless God confined the deep within bounds, the distinction between mountains and valleys, which contributes to the beauty of the earth, would cease to exist, for it would engulf the whole earth. It is said that God has founded a place for the valleys; for there would be no dry land at the foot of the mountains, but the deep would bear sway, did not God command the space there to be unoccupied by the sea, as it were contrary to nature.

Thou coveredst it with the deep as with a garment - Compare the notes at Job 38:9. The meaning is, that God covered the earth with the sea - the waters - the abyss - as if a garment had been spread over it. The reference is to Genesis 1:2; where, in the account of the work of creation, what is there called "the deep" - the abyss - (the same Hebrew word as here - תהום tehôm - covered the earth, or was what "appeared," or was manifest, before the waters were collected into seas, and the dry land was seen.
The waters stood above the mountains - Above what are now the mountains. As yet no dry land appeared. It seemed to be one wide waste of waters. This does not refer to the Deluge, but to the appearance of the earth at the time of the creation, before the gathering of the waters into seas and oceans, Genesis 1:9. At that stage in the work, all that appeared was a wide waste of waters.

Thou coveredst it with the deep - This seems to be spoken in allusion to the creation of the earth, when it was without form and void, and darkness was upon the face of the deep, and the waters invested the whole, till God separated the dry land from them; thus forming the seas and the terraqueous globe.
The poet Ovid has nearly the same idea: -
Densior his tellus, elementaque grandia traxit,
Et pressa est gravitate sua; circumfluus humor
Ultima possedit, solidumque coercuit orbem.
Met. lib. i., ver. 29.
Earth sinks beneath, and draws a numerous throng
Of ponderous, thick, unwieldy seeds along:
About her coasts unruly waters roar;
And, rising on a ridge, insult the shore.
Dryden.

Thou coveredst it with the (c) deep as [with] a garment: the (d) waters stood above the mountains.
(c) You make the sea to be an ornament to the earth.
(d) If by your power you did not bridle the rage of the waters, the whole world would be destroyed.

Thou coverest it with the deep as with a garment,.... This refers not to the waters of the flood, when the earth was covered with them, even the tops of the highest mountains; but to the huge mass of waters, the abyss and depth of them, which lay upon the earth and covered it as a garment, at its first creation, as the context and the scope of it show; and which deep was covered with darkness, at which time the earth was without form, and void, Genesis 1:2 an emblem of the corrupt state of man by nature, destitute of the image of God, void and empty of all that is good, having an huge mass of sin and corruption on him, and being darkness itself; though this depth does not separate the elect of God, in this state, from his love; nor these aboundings of sin hinder the superaboundings of the grace of God; nor the operations of his Spirit; nor the communication of light unto them; nor the forming and renewing them, so as to become a curious piece of workmanship; even as the state of the original earth did not hinder the moving of the Spirit upon the waters that covered it, to the bringing of it into a beautiful form and order.
The waters stood above the mountains; from whence we learn the mountains were from the beginning of the creation; since they were when the depths of water covered the unformed chaos; and which depths were so very great as to reach above the highest mountains; an emblem of the universal corruption of human nature; the highest, the greatest men that ever were, comparable to mountains, have been involved in it, as David, Paul, and others.

These verses rather describe the wonders of the flood than the creation (Genesis 7:19-20; 2-Peter 3:5-6). God's method of arresting the flood and making its waters subside is poetically called a "rebuke" (Psalm 76:6; Isaiah 50:2), and the process of the flood's subsiding by undulations among the hills and valleys is vividly described.

The deep - In the first creation, Genesis 1:2, Genesis 1:9.