Hebrews 7:20-24

And inasmuch as not without an oath he was made priest:

(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.