Which Keruvim are these?
Rashi: They are the Keruvim that Shlomo made; they stand on the ground. They are not the Keruvim on the Kapores (cover) on the Aron.
Were the Keruvim there before the Aron?
Radak: Yes. Betzalel's Aron with the Keruvim on it fit under the wings of Shlomo's Keruvim. Shlomo's Keruvim were 10 Amos tall 1 (6:26); the bodies themselves did not occupy space; it was miraculous.
Betzalel's Aron with the Keruvim fit in the Mishkan, which was 10 Amos tall. Chazal said that the Aron did not occupy space (Yuma 21a), but not that it was a miracle that it fit inside (like it says there about Shlomo's Keruvim. - PF)
Why does it elaborate to say "El Mekomo El Devir ha'Bayis El Kodesh ha'Kodoshim El Tachas Kanfei ha'Keruvim"?
Malbim: The relation of the Aron to the Mikdash is like the Neshamah (in the brain) to the body. (a) It is in its own place. (b) It reasons by itself while incarcerated in the body. (c) It sends its conclusions to illuminate the body and dispel the body's darkness. The three places mentioned allude to these three attributes.
Why did Shlomo make new Menoros, Shulchanos and Keruvim, but not a new Aron?
Radak: We cannot ask this. Everything was via prophecy - "ha'Kol bi'Chsav mi'Yad Hashem Alai Hiskil" (Divrei ha'Yamim I, 28:19).
