Hebrews 7:16 (KJV)

If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?

For the priesthood being changed, there is made of necessity a change also of the law.

For he of whom these things are spoken pertaineth to another tribe, of which no man gave attendance at the altar.

For it is evident that our Lord sprang out of Juda; of which tribe Moses spake nothing concerning priesthood.

And it is yet far more evident: for that after the similitude of Melchisedec there ariseth another priest,

For he testifieth, Thou art a priest for ever after the order of Melchisedec.

For there is verily a disannulling of the commandment going before for the weakness and unprofitableness thereof.

For the law made nothing perfect, but the bringing in of a better hope did; by the which we draw nigh unto God.

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:)