And they shall make for Me a sanctuary and I will dwell among them. (Shemot 25:8)
Our parasha discusses the construction of the Mishcan. The Mishcan was the portable sanctuary that accompanied Bnai Yisrael in the wilderness. Once Bnai Yisrael entered and conquered the Land of Israel, this Mishcan – Tabernacle – was replaced by a permanent structure. This structure was the Bait HaMikdash – the Sacred Temple – constructed by King Shlomo.
Our passage contains the specific command to construct the Mishcan. However, Maimonides indicates in his Sefer HaMitzvot that this passage is also the source for the commandment to build the Bait HaMikdash.  Sefer Mitzvot Gadol – SeMaG – agrees that there is a commandment to build the Bait HaMikdash. However, he objects to Maimonides’ contention that the mitzvah is derived from our pasuk. He suggests that the proper source for the commandment to build the Bait HaMikdash is a set of pasukim in Sefer Devarim. In these pesukim, Moshe tells Bnai Yisrael that they will cross over the Jordan and inhabit the Land of Israel. Moshe then tells the people that Hashem will choose a place for His Mikdash, and it is to that place that all sacrifices will be brought., 
Rav Yosef Karo suggests that there is an obvious reason for SeMaG’s rejection of Maimonides’ position. Our passage is not discussing the Bait HaMikdash. It is specifically commanding the construction of the Mishcan. How can Maimonides contend that this passage is the source for the obligation to build the Bait HaMikdash?
It seems that SeMaG’s objection to Maimonides’ position is reasonable. Why does Maimonides insist on citing our passage as the source for the commandment to build the Bait HaMikdash? Rav Yosef Karo suggests that Maimonides’ position is based upon a problem within the wording of our passage. What is this problem?
In our pasuk, Bnai Yisrael are commanded to build a sanctuary for Hashem. There are two terms used in the Torah for “sanctuary.” These terms are Mishcan and Mikdash. The term Mishcan is generally used to refer to the Tabernacle of the wilderness. In our passage, Hashem directed Bnai Yisrael to build this Tabernacle of the wilderness. Therefore, it seems that the passage should have used the term, Mishcan. However, in our passage, Hashem does not tell Bnai Yisrael to build a Mishcan – a Tabernacle. He tells Bnai Yisrael to build a Mikdash. Why does the passage use the term Mikdash and not the seemingly more appropriate term Mishcan?
Rav Yosef Karo suggests that Maimonides is answering this question. According to Maimonides, the term Mikdash is a more general term than Mishcan. It includes both the Tabernacle and the Bait HaMikdash. The passage specifically uses the term Mikdash in order to include both forms of sanctuary – the portable Tabernacle, and the permanent Bait HaMikdash. It seems that according to Rav Yosef Karo, Maimonides maintains that our pasuk legislates the requirement to establish a sanctuary. This institution does not have a specific form. Instead, the structure of the sanctuary is flexible. This commandment includes the Mishcan constructed in the wilderness, and the Bait HaMikdash constructed by Shlomo.
How are these different structures included in one mitzvah? Sometimes it is appropriate for this sanctuary to be a portable structure. At other times, a permanent structure is more fitting. The environment in which the sanctuary will be placed determines its form. When Bnai Yisrael were traveling in the wilderness, the nation was not permanently situated. It was appropriate for the sanctuary to travel with the camp. Once Bnai Yisrael settled in the Land of Israel, the nation was permanently situated. At this point, a permanent structure became appropriate.
This is a reasonable explanation of Maimonides’ position. However, SeMaG raises an important objection to this position. The Midrash Sifri enumerates three commandments that came into effect when Bnai Yisrael entered the Land of Israel. These mitzvot are to appoint a king, to build a Mikdash, and to destroy Amalek. It seems that Sifri is asserting that the commandment to construct the Mikdash – a sanctuary – is comparable to the other two commandments mentioned by the Sifri. These other two commandments did not apply in the wilderness. Similarly, it appears that the commandment to build a Mikdash did not apply in the wilderness. Instead, the commandment first became operative with Bnai Yisrael’s conquest of the Land of Israel. It is interesting that Maimonides also quotes this midrash in his Sefer HaMitzvot. How can Maimonides’ position be reconciled with this Midrash?
Maimonides explains that there is a fundamental difference between the Mishcan and the Bait HaMikdash. He explains that the Mishcan was originally constructed in the wilderness and was intended to serve as a temporary structure. When the nation entered the Land of Israel, the Mishcan was established in Gilgal. It was then moved to Shiloh. The Mishcan was subsequently replaced by a sanctuary constructed in Nov. The Nov sanctuary was also eventually replaced by a sanctuary build in Givon. In turn, the sanctuary of Givon was replaced by the Bait HaMikdash. Once the Bait HaMikdash was constructed, its site became the permanent location for any subsequent sanctuary. The second Bait HaMikdash was constructed upon this location, and the third will also be built on this site. In short, all of the sanctuaries built before the Bait HaMikdash were temporary. These sanctuaries were erected at a site for a period of time and then moved to a new location and, sometimes, even replaced by a new structure. However, once the Bait HaMikdash was built upon the Temple Mount in Yesushalayim, this site became the permanent location of the structure.
This distinction reflects a fundamental difference between the sanctuaries that preceded the Bait HaMikdash and the Bait HaMikdash itself. As explained above, the institution of the sanctuary is expressed in different forms. In the wilderness, the sanctuary took the form of the Mishcan – a portable structure. The sanctuary took other forms once the nation entered the Land of Israel. However, all of the iterations of the sanctuary were innately temporary and precursors to the Bait HaMikdash. The Bait HaMikdash represents the ultimate and final form of the sanctuary. Once the Bait HaMikdash was built, it was the final form and site for the sanctuary. All subsequent sanctuaries are reconstructions of this King Shlomo’s Bait HaMikdash and built on its site.
This distinction between the Bait HaMikdash and its precursors resolves the contradiction between Maimonides’ position and the Sifri. Although versions of the sanctuary existed before the nation entered the Land of Israel, the final and ultimate fulfillment of the commandment to build a sanctuary could not be achieved until the Land of Israel was completely secured and the Bait HaMikdash was constructed.
Let us now reconsider the dispute between Maimonides and SeMaG. According to Maimonides, the mitzvah to build a sanctuary includes the Bait HaMikdash and all of its precursors. According to SeMaG, the commandment specifically instructs us to build the Bait HaMikdash. It does not include the precursor of the Bait HaMikdash. Why does SeMaG exclude the Mishcan from the commandment?
It seems that according to SeMaG, the Bait HaMikdash is a fundamental element of the sanctity of the Land of Israel. In other words, the sanctity of the Land of Israel has a specific structure. This sanctity requires that the Land of Israel include as a central element the Bait HaMikdash. The Mishcan and the other sanctuaries that preceded the Bait HaMikdash were places for the offering of sacrifices and the worship of Hashem. But, these structures were not expressions of the sanctity of the Land of Israel.
Maimonides disagrees. He argues that the commandment to build a sanctuary was given in the wilderness. It was first fulfilled through the construction of the Mishcan. According to Maimonides, the sanctuary is a central element within the national community of Bnai Yisrael. This community first emerged in the wilderness. With its emergence came the requirement to build this community around a sanctuary. The appropriate sanctuary for the nation as it traveled through the wilderness was the Mishcan. The structure of the national community evolved, and did not achieve its final form until the people possessed the Land of Israel. In other words, Bnai Yisrael evolved from a nomadic nation into a people with a land. As the national community evolved, the institution of the sanctuary evolved. Once the people achieved possession of the land, the nation became complete. The complete community required a permanent Bait HaMikdash. In short, Maimonides and SeMaG disagree on the framework of the sanctuary. According to SeMaG, the sanctuary is an expression of the sanctity of the Land of Israel. Therefore, the Mishcan and the Bait HaMikdash are fundamentally different institutions. According to Maimonides, the sanctuary is a fundamental element of the national community of Bnai Yisrael. Therefore, at different times in the history of Bnai Yisrael, the Mishcan and the Bait HaMikdash have served as appropriate expressions of this institution. Of course, Maimonides acknowledges that the Bait HaMikdash is the ultimate form of the institution of the sanctuary. However, this is because the nation of Bnai Yisrael is only complete once it is in possession of the Land of Israel.
 Rabbaynu Moshe ben Maimon (Rambam / Maimonides) Sefer HaMitzvot, Mitzvat Aseh 2.
 Sefer Devarim 11:10-11.
 Rabbaynu Moshe ben Yaakov of Coucy (SeMaG), Sefer Mitzvot Gadol, Mitzvat Aseh 163.
 Rav Yosef Karo, Rav Yosef Karo, Hilchot Bait HaBechirah 1:1.
 Rav Yosef Karo, Kesef Mishne, Hilchot Bait HaBechirah 1:1.
 Rabbaynu Moshe ben Yaakov of Coucy (SeMaG), Sefer Mitzvot Gadol, Mitzvat Aseh 163.
 Rabbaynu Moshe ben Maimon (Rambam / Maimonides) Sefer HaMitzvot, Mitzvat Aseh 20.
 Rabbaynu Moshe ben Maimon (Rambam / Maimonides) Mishne Torah, Hilchot Bait HaBeChirah 1:1-3.