"And they shall make for Me a sanctuary"—Exodus 25:8.
We are commanded to build a Sanctuary to serve [G‑d]. In it we offer sacrifices, burn the eternal flame, offer our prayers, and congregate for the festivals each year.
This is one of the three mitzvot the Jews were commanded to fulfill upon entering the Land—the other two being crowning a king and annihilating Amalek.
Included in this mitzvah are many details—e.g., building a menorah, a showbread table, altars.