John Gill Commentary Leviticus 7:34

"For the wave-breast and the heave-thigh have I taken of the children of Israel out of the sacrifices of their peace-offerings, and have given them unto Aaron the priest and unto his sons as [their] portion for ever from the children of Israel." — Leviticus 7:34 (ASV)

For the wave breast and the heave shoulder have I taken of
the children of Israel
These two parts were particularly pitched upon and selected:

from off the sacrifices of their peace offering ;
the rest being allowed the owners, besides what were burnt:

and have given them unto Aaron the priest and unto his sons, by a
statute for ever from among the children of Israel ;
as long as the priesthood lasted, even to the coming of the Messiah, in whom all these sacrifices would have their accomplishment and their end.