Moshe describes the desolation of the Land of Israel which will be a result of the failure to heed Hashem's mitzvos. Both their descendants and foreigners alike will remark on the singular desolation of the Land and its apparent inability to be sown or to produce crops. Moshe promises, however, that the people will eventually repent after both the blessings and the curses have been fulfilled. Then, however assimilated they have become among the nations, Hashem will bring them back to Eretz Yisrael. The Parsha concludes with a dramatic choice between life and death.
Moshe exhorts the people to choose life.
The answer is, that just as every potential branch is considered part of the tree from which it will one day grow, so too every Jew is bound by the acceptance of Torah, because his potential to exist was already rooted in his forefathers. Thus, since his forefathers accepted the Torah, it is as though he accepted it himself. So, in reality, each individual was there as well. For just as an animal has no taste for wisdom and intellectual discernment, preferring hay and straw, so too a person who centers himself on physicality finds things of the spirit without taste. Thus, Man is an amalgam of two elements as disparate as heaven and earth.