Now consider how great this man was, to whom even the patriarch Abraham gave a tenth of the spoils. And indeed those who are of the sons of Levi, who receive the priesthood, have a commandment to receive tithes from the people according to the law, that is, from their brethren, though they have come from the loins of Abraham; but he whose genealogy is not derived from them received tithes from Abraham and blessed him who had the promises.
Now beyond all contradiction the lesser is blessed by the better. Here mortal men receive tithes, but there he receives them, of whom it is witnessed that he lives. Even Levi, who receives tithes, paid tithes through Abraham, so to speak, for he was still in the loins of his father when Melchizedek met him.
Therefore, if perfection were through the Levitical priesthood (for under it the people received the law), what further need was there that another priest should rise according to the order of Melchizedek, and not be called according to the order of Aaron? For the priesthood being changed, of necessity there is also a change of the law. For He of whom these things are spoken belongs to another tribe, from which no man has officiated at the altar. For it is evident that our Lord arose from Judah, of which tribe Moses spoke nothing concerning priesthood. And it is yet far more evident if, in the likeness of Melchizedek, there arises another priest who has come, not according to the law of a fleshly commandment, but according to the power of an endless life. For He testifies: "You are a priest forever According to the order of Melchizedek"." Heb. 7:1-17, NKJ.