At verse 14, as well as here, notice is taken, that to the
   tribe of Levi, "Moses gave no inheritance," for so God had
   appointed.  Nu 18:20.  If they had been appointed to a lot
   entire by themselves, Moses would have served them first, not
   because it was his own tribe, but because it was God's, but
   they must be provided for in another manner; their habitation
   must be scattered in all the tribes, and their maintenance
   brought out of all the tribes, and God himself was the portion
   both of their inheritance and of their cup.

  18:7  De 10:9  18:1,2