Malbim: He tells how he heard the command to the Chayos; they are commanded about the Ofanim. They do not move them via physical contact, not via a force that pulls or pushes, rather, via voice and a spiritual intellectual command. (a) When they fly with their wings, which hints to miraculous conduct based on Hashem's will, above nature and the Ma'arachah. This command is "k'Kol Shakai" - from Hashem, who overrides the Ma'arachah via special Hashgachah. It is "k'Kol Mayim Rabim" - at the time of creation, Ru'ach Elokim hovered above the water (the creation; there was not a Ma'arachah yet). Also refer to 1:24:3:3, 1:24:4:4.

Rashi: Do not say that the sound of much water is soft - "k'Kol Shakai", like the voice explained in Tehilim "Kol Hashem ba'Ko'ach" (Tehilim 29:5).

Radak #1: It is a Gibor's voice -"mi'Shakai Yavo" (Yeshayah 13:6) "v'Hayah Shakai b'Tzarecha" (Iyov 22:25).

Radak #2: It is Hashem's voice; He is called Shakai. Also in the third vision, it says "k'Kol Kel Shakai b'Dabero" (10:5) - like when He spoke on Har Sinai "Kol Gadol" (Devarim 5:19). Below, it was heard "Ad he'Chatzer ha'Chitzonah" (10:5) - the border of the Bayis. Also at Har Sinai, even though it was a great voice, it was not heard outside of Machaneh Yisrael. Also every Nevu'ah, the one for whom it is designated, only he hears it.

Malbim: Refer to 1:24:1:1.

Rashi citing Targum Yonasan: The voice of their words, when they thank and bless their Master, like the voice of a camp of supreme angels.

Radak: Mulah is like Milah (word), but it hints to a strong word heard when many speak, "k'Kol Machaneh."

Malbim: "B'Lechtam" (when they go without flying, according to the Ma'arachah), the voice was like that of a Machaneh. This is only when the nation is arranged like an ordered army. On the one hand, they hear only one voice, of Hashem based on Hashgachah. On the other hand, they hear many voices - the laws of nature and its orders.

Rashi: They slacken from making noise.

Rashi citing Targum Yonasan: They silence their wings in front of Hashem's voice that comes out from above their heads to inform Nevi'im of their mission, like it concludes "va'Yhi Kol me'Al?" (25).

Rashi citing Tanchuma Kedoshim 6: When they are Omed (cease) praising, due to Tzadikim, so that Tzadikim will praise first.

Malbim: I explained (19) that when stars go from west to east, there are cessations. Sometimes they seem to stop in the middle of the orbit. Physicists attribute this to gravity of other stars that they encounter in their paths. This ceases them from the big path due to the sun's gravity. The Navi says that [the cessation] is due to the Chayos and Hashem's will. When the straight wings of the Chayos soften - they receive influence from Olam ha'Kisei, and then they slacken from moving the Ofan, for they move it only via power that they receive from the Raki'a above their heads, via their wings spread straight to the Raki'a. When this ceases, their wings soften and they do not receive power from above, they cease and the Ofanim cease with them - "uv'Amdam Ya'amodu" (21).