Numbers 18:20

In their land, i.e. in the land of the children of Israel, mentioned Numbers 18:13. You shall not have a distinct and separate portion of land, as the other tribes shall. The reason of this law was, partly, because God would have them wholly devoted to and employed in his service, and therefore; free from worldly encumbrances and businesses; partly, because God had abundantly provided for them otherwise by tithes and first-fruits and oblations of all sorts; partly, because God would have their worldly comfort and happiness depend singly upon him and his service, and so would; oblige them to use more zeal and diligence in the advancement of piety, even for their own interest, which was either better or worse as true religion flourished or decayed; see Judges 17:9,Judges 17:10; Judges 19:18; 2 Chronicles 13:0:; 2 Chronicles 30:22; 2 Chronicles 31:4; partly, that this might be a firm bond of hearty love and affection between the people and their teachers, the Levites, who, as they performed religious services for the people, so they received their subsistence from them; and partly, that by this means being dispersed among the several tribes, they might have the better opportunity for teaching and watching over the people, which was their duty, Deuteronomy 33:10; 2 Chronicles 30:22; Malachi 2:4-7.

I am thy part, i.e. I have appointed thee a liberal maintenance out of my oblations.