From Chapter Five of Rabbi Shloma Majeski’s Likkutei Mekoros Vol. 2. (Underlined text is the compiler’s emphasis
6. […] In this generation, the final generation of exile and the first generation or redemption, we are finishing and completing “our deeds and our service throughout the entire duration of exile” to transform Eretz HaAmim, the land of the Gentile nations of the world – even the lowest possible place of the Diaspora, the Lower Hemisphere (where Mattan Torah did not take place) – into Eretz Yisroel. By elevating the very lowest region, all other places of the Diaspora ascend.
Uplifting the world in this way is in virtue of “Beis Rabbeinu,” located in the Lower Hemisphere. Beis Rabbeinu is the place from which light shines forth to the rest of the world. Thus, the entire world (even the most remote corner) is transformed into Eretz Yisroel, in fulfillment of “In the future, Eretz Yisroel will extend to all the lands” and “In the future, Yerushalayim will extend to all of Eretz Yisroel.” All the synagogues and study halls of the entire world will adjoin to the Beis HaMikdash, the Holy Temple, with the true and complete redemption through Moshiach Tzidkeinu. The Moshiach (redeemer of the Jewish people) of our generation is the leader of the generation (as above, Section 5). The main thing, however, is that he is the leader of the teachings of Chassidus,* for the dissemination of the wellsprings of Chassidus outward (“when your wellsprings are spread outward,” reaching even the furthest possible distance, spanning the entire face of the earth) brings about the advent of Malka Meshicha.
The latter discussion brings to light the great virtue of Beis Rabbeinu, the Mikdash M’at ha’ikari – the main Miniature Sanctuary, of the final exile, “for it journeyed from Kadeish and settled there.” Thus, “It is the place of the future Mikdash itself”; the Mikdash of the future will be revealed there, and from there it shall return to Yerushalayim (as discussed above in Section 4).
7. This concept is also alluded to in the name of “Beis Rabbeinu” in our generation:
“Rabbeinu”: Both the first and second names of the Rebbe allude to the redemption. His first name, Yosef, is in the spirit of the verse, “It shall be on that day that the L-rd will add (yosif) [the effect of] His hand, a second time to acquire the rest of His people, who will remain from Assyria and from Egypt…and from the islands of the sea…and He shall gather (v’asaf) the lost of Israel, and the scattered ones of Yehuda He shall gather from the four corners of the earth” (Yeshayahu 11:11-12). His second name, Yitzchok, alludes to laughter and joy, which will achieve its quintessence in the true and compete redemption by Moshiach Tzidkeinu, as it is written, “then our mouths will be filled with laughter” – specifically “then,” referring to the Future Era,** when we will say (specifically) to Yitzchok “for you are our father.”
And Beis (Rabbeinu): The building address is 770*** [Eastern Parkway]. The name of Beis Rabbeinu, of course, comes from this number, for all Jews call Beis Rabbeinu “770.” 770 is the gematria of “paratza – you have burst forth,” in the spirit of the verse, “And you shall burst forth westward, eastward, northward, and southward.” This verse alludes to the fact that light shines forth from this building to all four directions of the world, and in a manner of bursting forth through boundaries, elevating all corners of the globe to the status of Eretz Yisroel (“In the future Eretz Yisroel will extend to all the lands”).
This particularly includes the fact that all synagogues and all study halls throughout the entire world become established in Eretz Yisroel and adjoined to the Beis HaMikdash, with the true and complete redemption through Moshiach Tzidkeinu. Regarding Moshiach it is said, “paratza alecha Perez,” and our Sages interpret that “this refers to Moshiach, as it is said, ‘the poretz will rise before you.’”
(From Kuntres Beis Rabbeinu Sh’B’Bavel, Seifer HaSichos 5752, pg. 472-473)
NOTES:
*To note that the teachings of Chassidus corresponds to the level of the Yechida of Torah (see On the Essence of Chassidus), which is connected with the yechida of the Jewish people, the soul of Moshiach Tzidkeinu (as above in Footnote 53)
**Which is not the case in the time of exile, “for it is prohibited for a man to fill his mouth with laughter in this world, as it is said, ‘then our mouths will be filled with laughter’” (Brachos 31a).
***To note the practice of great Jewish scholars to teach allusions and lessons in the service of G-d even from mundane matters, and the like (such as the number of a car in a train, which is [seemingly] arbitrary, how much more so is the number of a permanent structure something that carries significance), especially in our case, where the number became the name of the building, as discussed inside the text proper.