The Bris Of The Tzibbur

At the end of the tochacha, the possuk says  אֵ֩לֶּה֩ דִבְרֵ֨י הַבְּרִ֜ית אֲֽשֶׁר־צִוָּ֧ה ה אֶת־מֹשֶׁ֗ה לִכְרֹ֛ת אֶת־בְּנֵ֥י יִשְׂרָאֵ֖ל בְּאֶ֣רֶץ מוֹאָ֑ב מִלְּבַ֣ד הַבְּרִ֔ית אֲשֶׁר־כָּרַ֥ת אִתָּ֖ם בְּחֹרֵֽב.  What is the nature of this bris?  In Netzavim it explains, הנסתרות לה' אלקינו וְהַנִּגְלֹ֞ת לָ֤ׄנׄוּׄ וּׄלְׄבָׄנֵ֙ׄיׄנׄוּ֙ׄ עַׄד־עוֹלָ֔ם לַעֲשׂ֕וֹת אֶת־כׇּל־דִּבְרֵ֖י הַתּוֹרָ֥ה הַזֹּֽאת 'יןבי Chazal explain teaches us the principle of arvus that one is responsible for the actions of other Jews.  In other words, the bris of חורב was an obligation on every individual to keep the Torah but the bris of ערבות מואב gives an obligation on the obligations of others as well.  This is why the tochacha in Ki Tavo is said in a singular form but the one is Bechukosai is said in the plural form.  Why the difference?  Because the first tochacha is said to every single individual but the second one is said to the totality of Klal Yisrael.

Why was this the time to have a bris on arvus?  Because it is only at Har Grizim and Har Eval, inside of Eretz Yisrael that Klal Yisrael become a single unit.  It requires Eretz Yisrael to join Klal Yisrael to be one body (see Rogatchover Sanhedrin 43b, teshuva 143, tefillah 2:17, Avnei Nezer 314.)  As Klal Yisrael enter the land they are no longer mere individuals but become a collective unit with responsibilities for the tzibbur at large (based upon Rav Hershel Schachter on the parsha, article from Rav Yitzchak Ginsburgh.) 

Rashi says that the obligation of bikkurim started only after the land was fully conquered and divided.  Why should those that where already harvesting fruits wait so long?  The Rebbe (Likutay Sichos volume 9) says since bikkurim has to be brought as an expression of ושמחת בכל הטוב, one's simcha can't be complete until every Jew has received their portion in the land.  In Eretz Yisrael every has their own portion of land, every one has their own mission but in in comes together as one unit.  If one part is missing, the portion of every individual is lacking as well.