Hebrews 7:1

Therefore, in this general and primordial law of God, the observance of which, in the case of the tree’s fruit, He had sanctioned, we recognise en closed all the precepts specially of the posterior Law, which germinated when dis closed at their proper times. For the subsequent superinduction of a law is the work of the same Being who had before premised a precept; since it is His province withal subsequently to train, who had before resolved to form, righteous creatures. For what wonder if He extends a discipline who institutes it? if He advances who begins? In short, before the Law of Moses, written in stone-tables, I contend that there was a law unwritten, which was habitually understood naturally, and by the fathers was habitually kept. …

After him brake out a second heretical Theodotus, who again himself introduced a sister-sect, and says that the human being Christ Himself was merely conceived alike, and born, of the Holy Spirit and the Virgin Mary, but that He was inferior to Melchizedek; because it is said of Christ, “Thou art a priest unto eternity, after the order of Melchizedek.” For that Melchizedek, he says, was a heavenly Virtue of pre-eminent grace; in that Christ acts for human beings, being made their Deprecator and Advocate: Melchizedek does so for heavenly angels and Virtues. For to such a degree, he says, is he better than Christ, that he is ἀπάτωρ (fatherless), ἀμήτωρ (motherless), ἀγενεαλογητον (without genealogy), of whom neither the beginning nor the end has been comprehended, nor can be comprehended.

Eran. I think the words of the divine Apostle are as follows; “For this Melchisedec, 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 by interpretation king of righteousness, and after that also king of Salem, which is king of peace; without father, without mother, without descent, having neither beginning of days, nor end of life; but made like unto the son of God; abideth a priest continually.” I presume you spoke of this passage.

88. Let no man, therefore, when he beholds an order of human establishment, contend that in it resides the claim of Divinity; for even that Melchizedek, by whose office Abraham offered sacrifice, the Church doth certainly not hold to be an angel (as some Jewish triflers do), but a holy man and priest of God, who, prefiguring our Lord, is described as “without father or mother, without history of his descent, without beginning and without end,” in order to show beforehand the coming into this world of the eternal Son of God, Who likewise was incarnate and then brought forth without any father, begotten as God without mother, and was without history of descent, for it is written: “His generation who shall declare?”