Hebrews 7:21-24

(for those priests were made without an oath; but this with an oath by him that said unto him, The Lord sware and will not repent, Thou art a priest for ever After the order of Melchisedec:) By so much was Jesus made a surety of a better testament. And they truly were many priests, because they were not suffered to continue by reason of death: but this man, because he continueth ever, hath an unchangeable priesthood.