"in the land": I might think that all of the mitzvoth are to be performed outside of Eretz Yisrael. It is, therefore, written "to do in the land which the L-rd, the G-d of your fathers, gave you to inherit." I might then think that all of the mitzvoth are to be performed only in Eretz Yisrael. It is, therefore, written "all the days that you live upon the earth."
Now that Scripture has included (viz. "all the days that you live upon the earth" [i.e., even outside Eretz Yisrael]) and excluded (viz. "to do in the land" [i.e., only in Eretz Yisrael]), derive the rule from what is stated in this regard, (viz. Ibid. 2) "Destroy shall you destroy all the places where the nations worshipped." Just as (the mitzvah to destroy) idolatry is characterized by its devolving upon the "body" (of the observer), is not dependent upon the land, and obtains both in the land and outside of it, so, all such mitzvoth obtain both in Eretz Yisrael and outside of it, with the exclusion of arlah (viz. Vayikra 19:23) and kilayim (viz. Vayikra 19:19), (which are also forbidden outside the land). R. Eliezer says: Also (forbidden is) chadash (viz. Vayikra 23:10-14).