The Levites belong to Yahweh. This is a staple feature throughout all the Pentateuchal sources.
“The Levites shall be mine. I am Yahweh!”
But this is only because of the theology of redemption at play here: The Levites ransom the lives of Israel’s firstborns (see #145). This ransom theology is best stated in the Priestly source:
And Yahweh spoke to Moses, saying: “And I, behold, I have taken the Levites from among the children of Israel in place of every firstborn, the first birth of the womb from the children of Israel. And the Levites shall be mine, because every firstborn is mine! In the day that I struck every firstborn in the land of Egypt, I consecrated every firstborn in Israel to me, from human to animal. They shall be mine. I am Yahweh! (Num 3:11-13).
Thus instead of all male firstborns belonging to Yahweh, the Levites redeem them and it is thus the Levites who belong to Yahweh.
As a result, the Levites have no allotment in the promised land. They belong to Yahweh. In the Deuteronomic tradition it is for this reason as well that the Levites are granted the tithes, firstfruits, and donations—in lieu of having a portion of the promised land.
Although the same themes are present in the Priestly source, there is nevertheless an additional feature at play here which is unique to the Aaronid-run priesthood represented in P. And that is that since only an Aaronid can be priest, the remaining Levites are delegated to being servants to the Aaronids (Num 3:5-10). Their non-priestly function is to minister after the service of the Tent of Meeting. And it is for this reason in P that the Levites are granted tithes—for their service relevant to the Tent of Meeting.