The Rambam (Hilchos Beis Habchira 1:1) cites the pasuk from Parshas Teruma concerning the constructing of the Mishkan as the source for the mitzva to build a Beis Hamikdash. A fundamental purpose of the Beis Hamikdash, notes the Rambam, is to be able to visit Hashem three times a year on the Shalosh Regalim. Why does the Rambam single out the mitzvah of aliya l'regel as a primary reason for the Beis Hamikdash? There are daily Korbanos, Shabbos and Yom Tov Korbanos, and many mitzvos associated with the Beis Hamikdash. What is it about visiting on the Shalosh Regalim that elevates this mitzva to the very essence of what the Beis Hamikdash was built for?
According to the Rambam the obligation to build a Beis Hamikdash is derived from the pasuk- "V'asu li mikdash v'shachanti bsochum - They should make me a sanctuary and I will dwell in their midst." The word "v'shachanti" defines the essence of the Beis Hamikdash. Mikdash is synonymous with Mishkan which comes from the word lishkon- to dwell. Hashem's presence in the Mishkan and Beis Hamikdash is called Shechina, also derived from the word lishkon. What is the significance of the term lishkon and why does it encapsulate the message of the Beis Hamikdash?
The primary parsha that deals with aliyah l'regel is in Sefer Devarim at the end of Parshas Reah. There are several mitzvos in Parshas Reah that place aliyah l'regel in its proper context. Bnei Yisrael are about to enter Eretz Yisrael and disperse throughout the land. Much of Parshas Reah deals with the challenges that will arise from this new reality. It is no longer practical to bring a Korban every time one wants to eat meat. The Torah gives us a new heter- to slaughter and eat meat not as a Korban. We cannot travel to Yerushalayim all the time to eat our Maaser Sheni so the Torah permits us to redeem it and bring the money to Yerushalayim when possible. There are also potentially tragic consequences to being geographically distant from the Beis Hamikdash. The ir hanidachas- the city that becomes completely idolatrous- is described in Parshas Reah as being in "one of the cities Hashem gave you." Only far from the presence of Hashem could such a tragedy occur. We know that historically being physically distant from the Beis Hamikdash was a concern for the Jewish people. In Sefer Yehoshua, we read about how the tribes who lived on the other side of the Jordan River built their own mizbeach lest their children think they have no connection to Hashem and His Mikdash. The proliferation of bamos- private areas to offer Korbanos- during the period of the first Beis Hamikdash was a response to the fear of being distant geographically from Hashem. However, this response was absolutely prohibited by the halacha. What is the correct way to address this very real concern of physical distance creating a barrier between Hashem and the Jewish People now dispersed throughout Eretz Yisrael?
The mitzvah of aliya l'regel is the proper solution to this problem. Although we cannot live in physical proximity to the Beis Hamikdash throughout the year, our three yearly visits reinforce our connection to the Mikdash and to Hashem's Presence that dwells there. Hashem becomes our shachen (neighbor) for each Yom Tov. The geographic closeness forges a bond that lasts from regel to regel. Hashem's Presence in the Beis Hamikdash is referred to as the Shecina. Hashem dwells, so to speak, in the Beis Hamikdash and we come to be His neighbors. The Mishkan that was physically accessible to the Jewish People who encamped around it at all times was replaced by a Mikdash which at times would be physically remote. The Miskan dimension was retained, however, through the mitzvah of aliyah l'regel.
The Rambam saw in the mitzvah of aliya l'regel not just another mitzvah associated with the Beis Hamikdash, but the very purpose of the Beis Hamikdash, that purpose being to be a place of Shechina- a place for a people dispersed throughout the land to become close to Hashem physically and, ultimately, spiritually.
During the period of the first Beis Hamikdash the disruption of aliyah l'regel by Yeravam ben Nevat brought about tragic consequences. The Northern tribes who were prevented from visiting the Beis Hamikdash three times a year eventually lost their connection to Hashem. Rampant Avoda Zara eventually brought about the exile of the Ten Tribes.
We turn to Hashem asking Him to return His Shechina to Yerushalayim. May we once again merit to visit Hashem in His Beis Hamikdash and thereby remain close to Him throughout our lives.