"770." This number in Gematria is "Paratzta," derived from "You shall spread out [U'Faratzta] west and east and north and south." This indicates that from this house light will go forth to all four corners of the world, in a manner of breaking through barriers, so that all four corners of the world will be elevated to the status of the land of Israel. (In the future the land of Israel will extend to all the lands.) This means in particular that all the synagogues and study halls throughout the world will be established in the land of Israel and connected to the Beis HaMikdash in the true and complete Redemption through our righteous Moshiach. For about him it says, "You have broken barriers for yourself," which our Sages of blessed memory explain as follows: "This is Moshiach, about whom it is said, 'The breaker is come up before them.'"
...In the completeness of the number seven (seven hundred and seventy) can also be found an allusion to the completeness of the Divine service of our Rebbe during his complete lifetime of seven decades, seventy years (5640-5710). His Divine service was concluded and completed in the lower hemisphere in the seventh decade (from the house whose number is seven hundred seventy). [This completeness] includes as well the extension of his Divine service in the years afterwards, through the seventh generation - "all sevenths are beloved."
Through this [extension] is accomplished the completion of our actions and Divine service during the time of exile in all seven continents of the world. Immediately and imminently "the L-rd shall continue to apply [yoseef] His hand a second time, etc., and He shall gather [Asaf] the lost of Israel, etc." In this way, "You have broken (in Gematria, seven hundred and seventy) barriers for yourself," "The breaker is come up before them."
All this receives added emphasis in this last period: The Divine service of spreading Torah and Judaism and the wellsprings outward from "Beis Rabbeinu" ("770") has continued and expanded with greater vigor and greater strength, even after (the last ten years of) his life in this world, for more than forty years (5710-5750). It has done so in a way that "G-d has given you a heart to know and eyes to see and ears to hear."
Thus we find that "Beis Rabbeinu" ("770") is a "fortress," "the mount that all mouths turn to," for more than a Yovel of years (5700-5750) - "Forever."
[That Beis Rabbeinu is a "fortress"] receives further emphasis when we see with our own eyes the many Jewish people, and the increasing numbers of them, that come to "Beis Rabbeinu," with greater vigor and greater strength, - "in the multitude of people is the splendor of the king" (which includes also "Who are the kings? the rabbis," and specifically the leader (king) of the generation). [The increase] has made it necessary to enlarge and expand "Beis Rabbeinu" further. The enlargement and expansion must be in a way that breaks through barriers, "Paratzta" (770 in Gematria), as if constructing a new building.
According to what was said previously concerning the pre-eminence of "Beis Rabbeinu Sh'b'Bavel" - that "the Temple traveled and settled there," and "this is the place of the actual Temple in the future," so that there the future Temple will be revealed and from there return to Yerushalayim - the great merit each and every Jew has in becoming a partner, physically and monetarily (and all who increase are praiseworthy) in building "Beis Rabbeinu Sh'b'Bavel" is obvious. And this is like a preparation for the actual descent and revelation of the future Temple, imminently and immediately.
(Pamphlet concerning "Mikdash M'at Zeh Beis Rabbeinu Sh'B'Bavel" - Sefer HaSichos 5752, p, 465)
