John Gill Commentary Numbers 5:9

"And every heave-offering of all the holy things of the children of Israel, which they present unto the priest, shall be his." — Numbers 5:9 (ASV)

And every offering of all the holy things of the children of
Israel
Of the holy sacrifices brought by them to be offered up; that part of them which is elevated, heaved, or waved, as the heave shoulder and wave breast:

which they bring unto the priest, shall be his ;
what they bring to him to offer for them shall be his who performs the service, even that part of them which is his due.