The reading is from St. Paul's Letter to the Hebrews 7:1-6

Brethren, Melchizedek, king of Salem, priest of the Most High God, met Abraham returning from the slaughter of the kings and blessed him; and to him Abraham apportioned a tenth part of everything. He is first, by translation of his name, king of righteousness, and then he is also king of Salem, that is, king of peace. He is without father or mother or genealogy, and has neither beginning of days nor end of life, but resembling the Son of God he continues a priest for ever. See how great he is! Abraham the patriarch gave him a tithe of the spoils. And those descendants of Levi who receive the priestly office have a commandment in the law to take tithes from the people, that is, from their brethren, though these also are descended from Abraham. But this man who has not their genealogy received tithes from Abraham and blessed him who had the promises.