(Bamidbar 18:20) "And the L-rd said to Aaron: In their land you will not inherit, and you will not have a portion in their midst. I am your portion and your inheritance in the midst of the children of Israel.": Why is (all of) this stated? Because it is written (Bamidbar 26:53) "To these shall the land be apportioned," I would think that all are included — Cohanim, Levites, Israelites, proselytes, women, bondsmen, tumtum (those of uncertain sex) and androgynous (hermaphrodites); it is, therefore, written: "And the L-rd said to Aaron: In their land you will not inherit" — This excludes (from inheritance) Cohanim." (Ibid. 23) "And in the midst of the children of Israel, they (the Levites) shall not inherit an inheritance" — This excludes Levites. (Ibid. 26:55) "By the names of the tribes of their fathers shall they inherit" — This excludes bondsmen and proselytes (Ibid. 54) "A man, according to his numbers shall his inheritance be given" — This excludes tumtum and androgynous. (Ibid. 18:20) "And the L-rd said to Aaron: In their land you will not inherit" — in the division of the land. "and you will not have a portion in their midst" — ("a portion") of the spoils.
"I am your portion and your inheritance" — At My table (i.e., from the sacrifices) you eat and at My table you drink. An analogy: A king gave gifts to (all of) his sons except one, saying to him: My son, I gave you a gift. At My table you eat and at My table you drink. And thus is it written (Vayikra 6:10) "Their portion have I given to them from My fire-offerings." (Devarim 18:1) "The fire-offering of the L-rd and His inheritance shall they eat."
Twenty-four priestly gifts were given to the Cohanim, twelve in the sanctuary and twelve in the borders (i.e., outside of Jerusalem.) Twelve in the sanctuary: sin-offering, guilt-offering, the remnant of the log of oil of the leper, the remnant of the omer, the two loaves, the show-bread, the remnant of meal-offerings, the terumah of the thank-offering (viz. Vayikra 7:14), the terumah of breast and thigh, the shoulder of the ram of the Nazirite.