Mikdash comes from the root kadash, to set apart, the same root as kadosh. It names the set-apart place, and its charter is a single sentence in Exodus 25:8: v'asu li mikdash v'shachanti b'tocham, let them make Me a sanctuary, that I may dwell in their midst. The stated purpose of the only sanctuary HaShem ever commissioned is His nearness. In their midst. The set-apartness of the place served the closeness of the Presence.

That is worth sitting with, because English church vocabulary borrowed the word and moved it. The room where a modern congregation meets is called the sanctuary, and the name carries the Exodus charter whether the building knows it or not. A mikdash exists so that He may dwell in the middle of the people. A room where everything flows from a platform at the front, where one man speaks and the rest receive, is set up for the opposite of in-their-midst, and the name on the sign becomes testimony against the architecture.

The prophets keep the word's promise pointed forward. Ezekiel 37:26-28 stakes the covenant future on it: I will set My mikdash in their midst forevermore, My dwelling place shall be with them. The word never migrates to meaning a lecture hall. From charter to consummation, a mikdash is where He is close.