Charles Ellicott 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)

By a statute for ever.— That is, the statute that these two parts of the peace offering are to be given to Aaron and his descendants who officiate at this sacrifice, is binding upon the Israelites as long as the priesthood lasts.