Genesis 14:18-20 Then Melchizedek king of Salem brought out bread and wine; he was the priest of God Most High. And he blessed him and said: "Blessed be Abram of God Most High, Possessor of heaven and earth; And blessed be God Most High, Who has delivered your enemies into your hand." And he gave him a tithe of all.
Hebrews 7:1-12 For this Melchizedek, king of Salem, priest of the Most High God, who met Abraham returning from the slaughter of the kings and blessed him, to whom also Abraham gave a tenth part of all, first being translated 'king of righteousness,' and then also king of Salem, meaning 'king of peace,' without father, without mother, without genealogy, having neither beginning of days nor end of life, but made like the Son of God, remains a priest continually. 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.