Hebrews 6:17-7:10 New Revised Standard Version (NRSV)
17 In the same way, when God desired to show even more clearly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it by an oath, 18 so that through two unchangeable things, in which it is impossible that God would prove false, we who have taken refuge might be strongly encouraged to seize the hope set before us. 19 We have this hope, a sure and steadfast anchor of the soul, a hope that enters the inner shrine behind the curtain, 20 where Jesus, a forerunner on our behalf, has entered, having become a high priest forever according to the order of Melchizedek.
The Priestly Order of Melchizedek
7 This “King Melchizedek of Salem, priest of the Most High God, met Abraham as he was returning from defeating the kings and blessed him”; 2 and to him Abraham apportioned “one-tenth of everything.” His name, in the first place, means “king of righteousness”; next he is also king of Salem, that is, “king of peace.” 3 Without father, without mother, without genealogy, having neither beginning of days nor end of life, but resembling the Son of God, he remains a priest forever.
4 See how great he is! Even[a] Abraham the patriarch gave him a tenth of the spoils. 5 And those descendants of Levi who receive the priestly office have a commandment in the law to collect tithes[b] from the people, that is, from their kindred,[c] though these also are descended from Abraham. 6 But this man, who does not belong to their ancestry, collected tithes[d] from Abraham and blessed him who had received the promises. 7 It is beyond dispute that the inferior is blessed by the superior. 8 In the one case, tithes are received by those who are mortal; in the other, by one of whom it is testified that he lives. 9 One might even say that Levi himself, who receives tithes, paid tithes through Abraham, 10 for he was still in the loins of his ancestor when Melchizedek met him.