Commentary for Genesis 1:9

"And G-d made the firmament" - and it was that when some of the elemental water was removed from under that part of the waters which became vaporous in nature, as it was when He said, "let the waters be gathered from beneath the heavens" Genesis 1:9, it was fit that the vaporous part would descend to that same place from which the that [non-vaporous portion of] waters was removed. But He made it such that that "firmament" that separates would have the power to stop and prevent the vaporous portion from descending - that's the "waters which are above the firmament", such that the transformed atmospheric portion would descend, while the vaporous would remain in its original place. Because of this, when the moist vapor reaches it [i.e., the firmament], it condenses and gives rise to rain, snow and hail. As they condense they descend, as it is said, "at the sound of His placing an abundance of water in the heavens" Jeremiah 10:13. - what it wanted by saying "heavens": the firmament which condenses the atmospheric part [of the waters], as it is said "And G-d called the firmament "heavens" Genesis 1:8. Now when the cloudy, excited vapor arrives there [at the firmament], it generates thunder and lightning, and it is said: "He lifts up clouds from the ends of the earth, thunder from the rain He makes" [continuation of verse quoted previously from Jeremiah]. Now, seeing as how some of the heavier watery element is above the lighter air, which from our perspectives is against their nature - this without doubt indicates the action of an volitional actor, intended such an outcome, as it is said, "the work of His hands shall the firmament declare" Psalms 19:2

יקוו המים THE WATERS SHALL BE DRAWN TOGETHER — For they were then spread over the surface of the whole earth, and He now gathered them together into what now constitutes the Ocean, which is the largest of all seas (Genesis Rabbah 5:2).

ויאמר אלוקים יקוו המים... אל מקום אחד, we already explained on verse 2 that the means employed to achieve this was the ruach, the wind. This is the reason why we were told already in verse 2 that “G’d’s wind (spirit) hovered over the expanse of the deep, something which occurred by making the rakia. (between heaven and earth) Now the water above the earth were concentrated in one region, location.