Hebrews 5:4-5
And no one takes the office upon himself, but men assume it only when called to it by God, as Aaron was.
Hebrews 5:10
since God pronounced him a high priest of the priesthood of Melchizedek.
Hebrews 7:11-14
Now if anything final had been really accomplished through the Levitical priesthood, for even the giving of the Law was based upon it, what further need would there have been of appointing a different priest of the priesthood of Melchizedek, instead of choosing one of the priesthood of Aaron?
Hebrews 7:23-28
The old priests too had to be numerous, because death prevented their continuing in office.