Why does it say "Ko Amar Hashem"?
Radak: He comes to rebuke Resha'im of his generation for offering Korbanos together with evil deeds, like he rebuked them at the beginning of the Sefer - "Lamah Li Rov Zivcheichem..." (1:11).
Malbim: Amidst discussing Yerushalayim that will be built in the future, he turns to his generation, who thought that the Mikdash atones for their sins, and they may do all abominations, as long as they appease for it via a Korban. It is impossible that the Mikdash, in which they offer to You Chelev and blood, will be destroyed 1 . He answers that the Mikdash and Korbanos oppose human intellect for three reasons. Refer to 66:1:2:5, 66:1:4:2, 66:2:1:3.
Surely they knew Tehilim (e.g. 79 and 137) that discuss the destruction of Yerushalayim (presumably, including the Mikdash)! Perhaps they thought that this could only be if they ceased offering Korbanos, e.g. in the days of Achaz. (PF)
What do we learn from "ha'Shamayim Kis'i veha'Aretz Hadom Raglai"?
Brachos 59a: Earthquakes occur when Hashem presses His legs under the Kisei ha'Kavod.
Chagigah 12a: This shows unlike Beis Hillel, who say that Hashem made Eretz before Shamayim. Does one make the footstool before the chair?! (Beis Shamai say that He made Shamayim first; Chachamim say, He made both of them at once.)
Kidushin 31a: If one transgresses in private, it is as if he presses the legs of the Shechinah 1 . .
Rashi: I do not need your Beis ha'Mikdash.
Radak, Malbim: Do you think that the Bayis where you bring Korbanos, that I dwell in it, and it can contain Me, like it contains a body? No - Shamayim is My chair, and the land is My footstool! This is like Shlomo said "Hine ha'Shamayim u'Shmei ha'Shamayim Lo Yechalkelucha Af Ki ha'Bayis ha'Zeh Asher Banisi" (Melachim I, 8:27). Radak - I did not command about the Bayis for Me to dwell in it, and not about the Korbanos in order to east them. I commanded only so Yisrael will prepare their hearts to Me, and they will have a special place to come to there to pray and offer Olos and Shelamim, to arouse their hearts to eradicate evil thoughts and burn them, like something burned on the Mizbe'ach. If so, if you do evil and come to My house and sacrifice in front of Me, you lost the intent. This is not My Mitzvah. It is the opposite of My desire. You anger Me. Shamayim is My throne (and not this house). 2
Rashi (31a): Sinning in private is like saying 'Hashem is not here.' Therefore, Hashem hides; it is as if the person presses the legs of the Shechinah and constricts Hashem, to say 'He is not here.' Me'iri, Ritva (31a) - he says that Hashem's honor is not here. It is as if he encroaches on His boundary. Ya'avetz - he hides from Him, and removes His Hashgachah from himself - "Pen Yir'eh Vecha Ervas Davar v'Shav me'Acharecha" (Devarim 23:15).
Radak: Hashem is not physical; "Kis'i" is a metaphor, like a king who sits on a throne, and his feet are on a stool, and He commands his nation what to do. Really, the throne is more honored than the footstool, therefore the throne is compared to Shamayim, and the footstool to the land.
Why does He say "what house will you build for Me"?
Rashi: What house can you build that will be proper for My Shechinah?
Malbim: Due to Hashem's spirituality, He cannot be contained in a place.
Why does it add "what is My place of rest"?
