The reading is from St. Paul's Letter to the Hebrews 7:7-17

BRETHREN, it is beyond dispute that the inferior is blessed by the superior. Here tithes are received by mortal men; there, by one whom it is testified that he lives. One might even say that Levi himself, who receives tithes, paid tithes through Abraham, for he was still in the loins of his ancestor when Melchizedek met him. Now if perfection had been attainable through the Levitical priesthood (for under it the people received the law), what further need would there have been for another priest to arise after the order of Melchizedek, rather than one named after the order of Aaron? For when there is a change in the priesthood, there is necessarily a change in the law as well. For the one of whom these things are spoken belonged to another tribe, from which no one has ever served at the altar. For it is evident that our Lord was descended from Judah, and in connection with that tribe Moses said nothing about priests. This becomes even more evident when another priest arises in the likeness of Melchizedek, who has become a priest, not according to a legal requirement concerning bodily descent but by the power of an indestructible life. For it is witnessed of him, "Thou art a priest for ever, after the order of Melchizedek."