Deuteronomy 18:1
“The levitical priests, the whole tribe of Levi, shall have no territorial portion with Israel.”
Their presence was required at the Temple, even according to a designated rotation of shifts; moreover, they were scattered amongst the territories of the tribes, in order to attend to the spiritual needs of the entire people. Thus, in acknowledgment of their devotion to H’Shem, Maimonides speaks of the optional commitment that we may take upon ourselves, to become like unto “spiritual Levites.”
The Tree of Life 