The 20th mitzvah is that 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, as will be explained.1

The source of this mitzvah is G‑d's statement2 (exalted be He), "Make a Sanctuary for Me."

The Sifri3 says, "The Jewish people were commanded three mitzvos upon entering Israel: appointing for them­selves a king, building themselves a Sanctuary and wiping out the descendants of Amalek." This wording ["three mitzvos"] shows clearly that building the Sanctuary is counted as a distinct mitzvah.

We have already explained4 that this general term ["Sanctuary"] in­cludes many parts. The Menorah, the Table, the Altar, etc. are all parts of the Sanctuary, everything together is called by the name, "Sanctuary," even though the Torah gives a distinct command for each indi­vidual element.

It is possible for one to entertain the thought that G‑d's statement5 regarding the Altar, "Make for Me an earthen Altar," constitutes a mitzvah separate from that regarding the Sanctuary.6 However, the explanation is as follows: The plain meaning of the verse refers to the era when it was permissible to bring sacrifices on a bamah, i.e. when we were allowed to construct an earthen altar and bring sacrifices upon it in any location.7 However, our Sages, may they rest in peace, explained that it is a commandment to build the altar attached to the ground, and that it cannot be moved around as it was in the desert. They explained this verse in the Mechilta of R. Yishmael8: "When you enter Israel, make for Me an altar attached to the ground." If so, this does apply to all generations.9

It — building an altar of stones — is considered an integral part of the Sanctuary. The Mechilta10 explains the verse "If you make for Me an earthen altar," as follows: "R. Yishmael says, 'Wherever the Torah uses the word im (if), it is not obligatory, with three exceptions. One exception is, "If (im) you make for Me an earthen altar," which is obligatory. How do we know it is really obligatory? From the verse,11 "You shall build the altar of Hashem your G‑d with whole stones."' "

All the details pertaining to this mitzvah — i.e. building the Sanctuary, its shape, its divisions, building the Altar, and all its regulations — are explained in the tractate which deals with it specifically, tractate Middos. The shape of the Menorah, the Table, the Golden Altar and their placement in the Sanctuary are explained in tractates Menachos12 and Yoma.13