In this week's Haftorah we read about Yeshaya's message to the people of Israel. We begin the Haftorah with a very powerful statement from God: "The heavens are my throne, and the earth is my footstool. What house could you build for me, what place could there be for me to rest in?" (66:1).
This rhetorical question, the Radak explains, is to make sure that B'nai Yisrael understand that the Beit HaMikdash is not God's house. The Radak tells us that the purpose of the Beit HaMikdash is that there needs to be a special place for prayer and for korbanot. In other words, "Don't think that you could ever actually build a house for me; I live in the Heavens and earth is only the place for my feet". Even that metaphorical footstool is so kadosh that we must erect a special building just for that purpose.
Contrast this view of the Beit HaMikdash with a previous view on The Purpose of the Mishkan. The Mishkan's purpose was to continue the ongoing revelation of Sinai. Why then the difference between the Mishkan and the Beit HaMikdash? The Mishkan is a moving caravan of nevua while the Beit HaMikdash is the home of the kedusha.
In Hilchot Yisodei HaTorah, the Rambam speaks about navua as a process. Even for Moshe who had no need for sleep, dreams and parables, or an angle - he still had to prepare himself for the nevua. Thus it seems that Moshe needed to have a moving place for this revelation, so that he could function as the leader, bringing BÂnai Yisrael through the desert, and a the navi at the same time.The Beit HaMikdash, on the other hand, it is easy to keep it distinct (kadosh) from the rest. Yeshaya's message here is to prevent the people from viewing the Beit HaMikdash has one would view a King's Palace. This is not the place where God dwells, this is only the place where my feet are and that place is kadosh enough to bring sacrifices to.