What is the Beit HaMikdash?

Because the Torah asks for one. 'Let them make Me a sanctuary' is followed by chapters of measurements, materials and procedures. Rambam counts building the House as a positive commandment that applies in every generation it can be fulfilled.

The Torah pairs the command with a reason: 'that I may dwell among them'. Among the people, not inside the building. Jewish commentators read it as a promise about a community, with a building as its focus.

Deuteronomy directs offerings to 'the place which the LORD your God shall choose' and forbids offering them anywhere else. Before Jerusalem, local altars were at times permitted; the Mishnah records that once the people came to Jerusalem, they were never permitted again.

Rambam states the law: after the Temple was built in Jerusalem, no other place is fit for a House of God or for offerings, for all generations. Synagogues are not temples, and nothing is offered in them.

The Torah itself never names the city. It speaks of 'the place' God will choose. The identification comes later in Scripture: David buys a threshing floor and builds an altar, declares 'this is the house of the LORD God', and Chronicles places Solomon's Temple on Mount Moriah, the name of the land where Abraham bound Isaac.

That the Temple mount and the mountain of the binding are one place is a tradition built on these verses. Rambam records it as received tradition. The Psalms add the theology: 'the LORD hath chosen Zion'.

Because the commandment to build did not end with the destruction, because the prophets describe a future House, and because Jewish law places rebuilding within the redemption. Rambam lists it among the acts of the messianic king.

Traditional Jewish sources do not treat rebuilding as a project for anyone to begin today at the present site. Most place it within a future that includes peace and the recognition of the nations.