Midrash su Levitico 25:34

6) Whence is it derived that one can "devote" his consecrations (i.e., that (the term) "cherem" can "take" upon his consecrations to the Cohein)? From "cherem holy." Whence is it derived that "cherem" can "take" upon his consecration of holy of holies? From "every cherem holy of holies." I might think that Cohanim and Levites can make "devotions"; it is, therefore, written "But" (to exclude this). These are the words of R. Yehudah. R. Shimon says: Cohanim do not "devote," for devotions revert to them. Levites can "devote," for devotions do not revert to them. Rebbi says: The words of R. Yehudah (that Cohanim and Levites cannot "devote") seem correct in respect to land, it being written (Vayikra 25:34) "for it (i.e., their land) is a perpetual holding for them" (and cannot be consecrated). And the words of R. Shimon (that Levites can "devote") seem correct in respect to movable objects, for devotions do not revert to them.

9) (Vayikra 25:34) ("But the field of the open place of their cities shall not be sold, for it is a perpetual holding for them.") Whence is it derived that a field may not be made an open place, nor an open place a field; that an open place may not be made a city, nor a city an open place? From "the field of the open place of their cities." R. Elazar said: Whereof is this said? Of the cities of the Levites; but in the cities of the Israelites a field may be made an open space, an open space may be made a field; an open space may be made a city, but a city may not be made an open space, so that the cities of Israel not be destroyed. "shall not be sold": "shall not be sold" by the Temple treasurer, or "shall not be sold" at all (vis-à-vis returning on Yovel and being redeemable even within the first two years)?

9) (Vayikra 25:34) ("But the field of the open place of their cities shall not be sold, for it is a perpetual holding for them.") Whence is it derived that a field may not be made an open place, nor an open place a field; that an open place may not be made a city, nor a city an open place? From "the field of the open place of their cities." R. Elazar said: Whereof is this said? Of the cities of the Levites; but in the cities of the Israelites a field may be made an open space, an open space may be made a field; an open space may be made a city, but a city may not be made an open space, so that the cities of Israel not be destroyed. "shall not be sold": "shall not be sold" by the Temple treasurer, or "shall not be sold" at all (vis-à-vis returning on Yovel and being redeemable even within the first two years)? It is, therefore, written "for it is a perpetual holding for them." How, then, am I to understand "shall not be sold"? As "shall not be sold" by the Temple treasurer. "it is … for them." (See end of 8 above)