Radak: Shamayim is a Klal for all the Galgalim (spheres on which Heavenly bodies are fixed). Ma'alosav are the nine Galgalim, one l'Ma'alah (above) another.

Radak citing Ibn Ezra: Shamayim is air; Ma'alosav are the three Yesodos. They are Galgalim, one above another.

Avos 3:6: If five engage in Torah, the Shechinah is among them.

Chagigah 12a: This shows that Hashem created the land before Shamayim. One does not build an Aliyah before the house!

Rashi #1: The collection of His creations [is founded on the ground].

Rashi #2: The gatherings of the straight, this was the foundation of the land for the fixing of Shamayim. Everything exists for the straight!

Radak: Agudaso is the fire, Ru'ach and water which are one bundle, one above the other, and they are on the land. It mentions the creation of the entire world, above and below - how do [people] not fear Him, and how can they [try to] hide from in front of His eyes?! He created the entire world, and judges and oversees everything - "Hashem Tzevakos" (5)! He created everything, and destroys everything when He desires. The land that He established on its bases, and those who dwell on it - if they will sin greatly, He will destroy His building, like He did in the flood, and Sedom and Amorah! All is in his Hand, like clay in the potter's hand. He makes a Kli, destroys it and makes a different Kli (Yirmeyah 18:4).

Radak citing Ibn Ezra: Agudaso are the living; Al Eretz Yesadah - they are like Agudos.

Malbim: This is like "ha'Mekareh va'Mayim Aliyosav...; Yasad Eretz Al Mechoneha" (Tehilim 104:3, 5). Initially, the entire world was water in water. When Hashem wanted the dry land to be seen, He stretched Shamayim like a curtain. I.e. He made the nature of water to rise in vapors to the Raki'a - the precipitation cycle. Water rises to the clouds, and remains there - via this, the dry land was revealed and the mountains rose from the Tehom - "Yasad Eretz Al Mechoneha." Our verse teaches that via building Ma'alosav in Shamayim (of water and vapors), Agudaso Al Eretz Yesadah - the dry land was founded.

Rashi citing Targum Yonasan: He said to gather camps numerous like water of the sea ¹ .

Radak: Hashem does opposite actions - He builds and destroys (refer to 9:6:2:5). Also water of the sea - He calls it and spills it on the ground!

Malbim: "Samti Gevul la'Yam Chak Olam v'Lo Ya'avrenhu" (Yirmeyah 5:22). He Himself stops the water from covering the dry land. He calls to the water and spills it on the land, and it returns to be water on water, like He did in Dor ha'Mabul.