Psalms 104:4-9

Verse 4 עשה מלאכיו רחות oseh rnalachaiv ruchoth, משרתיו אש להט mesharethaiv esh lohet.

The elements are described as prompt and expedite to perform the Divine commands, like angels or ministers serving in the tabernacle; the Hebrew word משרתיו mesharethaiv being a word most common in the sacred ministrations.
Verse 5 יסד ארץ על מכוניה yasad erets al mechonepha, בל תמוט עולם ועד bal tammot olam vaed. "Laying the earth upon its foundations,

That it should not be shaken for evermore."

This image Bishop Lowth thinks evidently taken from the tabernacle, which was so laid upon its foundations that nothing could move it, and the dispensation to which it was attached, till the end purposed by the secret counsel of God was accomplished: and thus the earth is established, till the end of its creation shall be fully answered; and then it and its works shall be burnt up. On the above ground, the stability of the sanctuary and the stability of the earth are sometimes mentioned in the same words.
Verse 6

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.
Verse 7

At thy rebuke they fled - When God separated the waters which were above the firmament from those below, and caused the dry land to appear. He commanded the separation to take place; and the waters, as if instinct with life, hastened to obey.

At the voice of thy thunder - It is very likely God employed the electric fluid as an agent in this separation.
Verse 8

They go up by the mountains; they go down by the valleys - Taking the words as they stand here, springs seem to be what are intended. But it is difficult to conceive how the water could ascend, through the fissures of mountains, to their tops, and then come down their sides so as to form rivulets to water the valleys. Most probably all the springs in mountains and hills are formed from waters which fall on their tops in the form of rain, or from clouds that, passing over them, are arrested, and precipitate their contents, which, sinking down, are stopped by some solid strata, till, forcing their way at some aperture at their sides, they form springs and fountains. Possibly, however, vapours and exhalations are understood; these by evaporation ascend to the tops of mountains, where they are condensed and precipitated. Thus the vapours ascend, and then come down to the valleys, forming fountains and rivulets in those places which the providence of God has allotted them; that is, continuous valleys, with such a degree of inclination as determines their waters to run in that direction till they reach another river, or fall into the ocean.

Some have thought there is a reference to the breaking up on the fountains of the great deep, at the time of the flood; while the protrusion of the waters would raise the circumambient crust, so as to form mountains, the other parts, falling in to fill up the vacuum occasioned by the waters which were thrown up from the central abyss, would constitute valleys.

Ovid seems to paraphrase this verse: -

Jussit et extendi campos, subsidere valles,

Fronde tegi sylvas, lapidosos surgere montes.

Met. lib. i., ver. 43. "He shades the woods, the valleys he restrains

With rocky mountains, and extends the plains."

Dryden.
Verse 9

Thou hast set a bound that they may not pass - And what is this bound? The flux and reflux of the sea, occasioned by the solar and lunar attraction, the rotation of the earth on its own axis, and the gravitation of the waters to the center of the earth. And what is the cause of all these? The will and energy of God. Thus the sea is prevented from drowning the earth equally where there are flat shores as where the sea seems hemmed in by huge mounds of land and mountains. The above, not these, are the bounds which it cannot pass, so that they cannot turn again to cover the earth.
Copyright information for Clarke