Charles Ellicott Commentary Numbers 18:20

"And Jehovah said unto Aaron, Thou shalt have no inheritance in their land, neither shalt thou have any portion among them: I am thy portion and thine inheritance among the children of Israel." — Numbers 18:20 (ASV)

Thou shalt have no inheritance ... — Aaron is addressed in this verse as the representative of the priesthood. He himself did not enter into the land of Canaan.

I am thy part and thine inheritance ... — All who are admitted into the number of Christ’s royal priesthood have God for their portion and inheritance—in life, in death, and throughout eternity (Psalms 142:5).