8 Hashem spoke further to Aharon: I hereby give you charge of My gifts, all the sacred donations of the Israelites; I grant them to you and to your sons as a perquisite, a due for all time.
18:8 I grant them to you and to your sons as a perquisite
The gifts and tithes presented to the Kohanim and Leviim are additional examples of commandments that apply only in the Land of Israel. Like the portion of challah (Numbers 15:17-21), these are gifts given to the spiritual leaders of Israel to provide for their physical sustenance in exchange for the spiritual sustenance they offered to the people. Since they have no portion of land of their own, the Kohanim and Leviim are dependent on the rest of the nation for their physical nourishment, while the spiritual work that they do elevates everyone else’s existence in the land.