Midrash su Levitico 7:34

5) (Vayikra 7:34) ("For the breast of the tenufah and the shok of the terumah have I taken from the children of Israel from the sacrifices of their peace-offerings, and I have given them to Aaron the Cohein and to his sons as an everlasting statute from the children of Israel.") "the breast": This is the breast (itself); "hatenufah": This is (to include as reverting to the Cohein what is added in the offering of the ram of the Nazirite in) the tenufah of the basket (viz. Numbers 6:19). "shok": This is the shok itself. "haterumah": This is (to include as reverting to the Cohein the terumah of the four challoth of the thanksgiving offering (viz. Vayikra 7:14). "have I taken from the children of Israel": They should have reverted to the (first-born of the) Israelites, (who were originally slated to be the priests), but when they sinned (with the golden calf), they were taken from them and given to the Cohanim. I might think that just as they were taken from them because they sinned, so they will be restored to them (in the future, when their sin is atoned). It is, therefore, written "and I have given them to Aaron the Cohein and to his sons as an everlasting statute" — They are given to the Cohein as an everlasting gift.

6) I might think that the offerings, too, should be subject to the (priestly) gifts (shoulder, cheeks, and maw, viz. Devarim 18:3), and that it follows a fortiori, viz.: Now if chullin (non-consecrated food), which is not subject to the giving of breast and shok (to the Cohein), is subject to the (priestly) gifts (above), then the offerings, which are subject to the giving of breast and shok, how much more so should they be subject to the (priestly gifts! It is, therefore, written "and I have given them (breast and shok) to Aaron the Cohein and to his sons" — only those that are referred to in that context. "from the children of Israel": (only) by the consent of all of Israel (to give them to the Cohanim from their peace-offerings, i.e., the Cohanim may not seize them by force).

(Bamidbar 6:20) "And the Cohein shall lift them, a lifting before the L-rd": back and forth and up and down, as it is written (Shemot 29:27) "which was waved and which was lifted." Lifting is being compared to waving. Just as waving is back and forth, so, lifting; and just as lifting is up and down, so, waving — whence they ruled: the mitzvah of waving — back and forth, up and down. (Ibid.) "before the L-rd": in the east. For wherever "before the L-rd" is written, in the east is understood unless it is specified otherwise. "It is holy to the Cohein, in addition to the breast of waving and the thigh of lifting": Why is this stated? (i.e., it is already written [Vayikra 7:34]) "For the breast of waving, etc.") For in "For the breast of waving and the thigh of the lifting have I taken from the children of Israel from their peace-offerings," the peace-offerings of the Nazirite are also subsumed, and Scripture (here) removed them from their context for the ram's shoulder requirement. This tells me only of the latter. Whence do I derive (the same for) the breast and the thigh? It follows a fortiori, viz.: If individual peace-offerings, which do not require the giving (to the Cohein) of the shoulder, do require the (giving of) breast and thigh, then the Nazirite peace-offerings, which do require the giving of the shoulder, how much more so do they require the giving of breast and thigh! Now if I can derive this a fortiori, why need it be written (Ibid.) "It (the shoulder) is holy to the Cohein, in addition to the breast of waving and the thigh of lifting"? We are hereby apprised that every thing (in this instance, Nazirite peace-offerings) which was included in a general formulation and departed from that formulation for the sake of a new learning (in this instance, the giving of the shoulder) may not be returned to its general formulation until Scripture explicitly does so.

I might think that even all offerings (i.e., individual peace-offerings) were subject to priestly gifts, and that this followed a fortiori, viz.: If chullin (non-consecrated animals), which are not subject to (the giving to the Cohein of) breast and thigh, are subject to priestly gifts (of chullin), then consecrated animals, which are subject to breast and thigh, how much more so should they be subject to priestly gifts! It is, therefore, written (Vayikra 7:34) "and I have given them (breast and thigh) to Aaron the Cohein." Nothing in addition to what is stated herein. I might think that chullin, too, are subject to (the giving to the Cohein of) breast and thigh, and that it follows a fortiori, viz.: If consecrated animals, which are not subject to priestly gifts (shoulder, cheeks, and maw), are subject to breast and thigh, then chullin, which are subject to priestly gifts, how much more so should they be subject to breast and thigh! It is, therefore, written "And this (shoulder, cheeks, and maw) shall be the judgment of the Cohanim."