Hebrews 7:4-6, 9-12

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.

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.