Rabbi Hershel Schachter
Am Yisroel Chai
In the concluding possuk of the haftorah of Parshas Bo, the navi Yimriyahu speaks of the rise and fall of all civilizations except for "my servant Yaakov". The Jewish people is eternal.
The medrash comments on Yaakov's dream (in the beginning of Parsha Vayeitzei) where he saw the angels climbing up and down the ladder, that these angels represented the "guiding angels" of each of the nations of the world; and that each nation will have a natural progression of rising and falling, except for Klal Yisroel which will not disappear (see Jewish History: Stranger than Fiction). The navi Malachi (3:6) also predicts benevuah that "atem bani Yaakov lo chlisem". The Talmud (Bava Basra 116b) states that it is not only inconceivable for the entire Klal Yisroel to disappear, but even for an entire shevet. The Raavad (in his peirush on the Sifra on Parshas Bechukosai) explains that this is based on the principle that each and every shevet is referred to by the Torah as a "kahal" (see Talmud Huriyos 4b)!
Rambam (Sefer Hamitzvos aseh #153) adds a very interesting comment to these prophecies. Not only did G-d promise that there would always be individual survivors following whatever holocaust might occur, but more than that: Hakadosh Baruch Hu promised that "Klal Yisroel" would survive. Rambam takes that to mean that there would always remain at least a minyan of Jews living in Eretz Yisroel. For, if one were to imagine, chas veshalom, that there would only be millions of Jews living all over the world, but no Jews living in Eretz Yisroel, that would mean, by definition, that Klal Yisroel had ceased to exist. All the Jews who live outside Eretz Yisroel are only considered as individuals. Only those who live in Eretz Yisroel constitute Klal Yisroel.
Rambam further explains (in his commentary to Mishnayos Bechoros 29) that we have several halachos which are based on this premise.
Semicha can only be conferred in Eretz Yisroel, because this is not a private matter. One who himself has semicha can confer it upon others only as a representative of Klal Yisroel. The semicha is really conferred by Klal Yisroel; since only those who live in Eretz Yisroel constitute Klal Yisroel, therefore the act of conferring semicha must take place only in Eretz Yisroel. (The institution of semicha which we have today is only rabbinic in nature, and is basically only an imitation of the authentic biblical semicha which exited years ago. See Rama to Shulchan Aruch Yoreh Deah 242:14).
When determining whether the majority of Klal Yisroel had sinned (with respect to bringing the special communal korban, par he'elem davar shel tzibbur) the Talmud (Huriyos 3a) derives from Tanach that the tzibbur only includes those who live in Eretz Yisroel.
Similarly, Rambam writes, this is the reason that the beth din authorized to establish Rosh Chodesh must convene in Eretz Yisroel. This beth din doesn't really act as on its own, but rather as a representative of Klal Yisroel. Klal Yisroel was empowered to establish the Roshei Chodoshim, and the concept of Klal Yisroel only relates to those who live in Eretz Yisroel.