What is the meaning of "Solu"?
Rashi: It is an expression of praise. The same applies to "Lo Sesuleh b'Chesem" (Iyov 28:16), "ha'Mesul'aim ba'Paz" (Eichah 4:2).
Radak: Elevate. This is like "Salselah u'Sromemecha" (Mishlei 4:8). Every expression of Salal is elevation.
Malbim: Clear a path - "Yashru ba'Aravah Mesilah lEi'lokeinu" (Yeshayah 40:3).
What is "la'Rochev ba'Aravos"?
Radak: This is like "Rochev Shamayim" (Devarim 33:26). Just like the rider makes the animal go, so Hashem rotates the Galgal (spherical shell that houses the Heavenly bodies), Aravos is the top sphere that surrounds all the spheres and makes them move (rotate) via its motion.
Malbim: He depicts Hashem like a warrior riding on his horse; His chariot is salvation. The place of His chariot is in the Midbar, for there He rides to fight His enemies.
Why does it say "b'Kah Shmo"?
Rashi: It is an expression of fear. The Targum of "Avi v'Zimras Kah" (Shemos 15:2) is Dechilah, and also of "Ki Yad Al Kes Kah" (Shemos 17:16). One should praise, fear and rejoice. This is like it says above "v'Gilu bi'R'adah (2:11).
Radak: Elevate Him via 'Kah', which is His name, and indicates that He created the world 1 and caused it to exist.
Malbim: This name indicates His Gevurah; it rides with Him to fight His enemies.
Menachos 29b: He created the world to come with the letter Yud, and this world with the letter Hei.
Where should they rejoice in front of Him?
Radak: In the Beis ha'Mikdash.
