1 But again, those who assert that He was simply a mere man, begotten by Joseph, remaining in the bondage of the old disobedience, are in a state of death having been not as yet joined to the Word of God the Father, nor receiving liberty through the Son, as He does Himself declare: “If the Son shall make you free, you shall be free indeed.” But, being ignorant of Him who from the Virgin is Emmanuel, they are deprived of His gift, which is eternal life; and not receiving the incorruptible Word, they remain in mortal flesh, and are debtors to death, not obtaining the antidote of life. To whom the Word says, mentioning His own gift of grace: “I said, You are all the sons of the Highest, and gods; but you shall die like men.” He speaks undoubtedly these words to those who have not received the gift of adoption, but who despise the incarnation of the pure generation of the Word of God, defraud human nature of promotion into God, and prove themselves ungrateful to the Word of God, who became flesh for them. For it was for this end that the Word of God was made man, and He who was the Son of God became the Son of man, that man, having been taken into the Word, and receiving the adoption, might become the son of God. For by no other means could we have attained to incorruptibility and immortality, unless we had been united to incorruptibility and immortality. But how could we be joined to incorruptibility and immortality, unless, first, incorruptibility and immortality had become that which we also are, so that the corruptible might be swallowed up by incorruptibility, and the mortal by immortality, that we might receive the adoption of sons?
2. For this reason [it is, said], “Who shall declare His generation?” since “He is a man, and who shall recognise Him?” But he to whom the Father which is in heaven has revealed Him, knows Him, so that he understands that He who “was not born either by the will of the flesh, or by the will of man,” is the Son of man, this is Christ, the Son of the living God. For I have shown from the Scriptures, that no one of the sons of Adam is as to everything, and absolutely, called God, or named Lord. But that He is Himself in His own right, beyond all men who ever lived, God, and Lord, and King Eternal, and the Incarnate Word, proclaimed by all the prophets, the apostles, and by the Spirit Himself, may be seen by all who have attained to even a small portion of the truth. Now, the Scriptures would not have testified these things of Him, if, like others, He had been a mere man. But that He had, beyond all others, in Himself that pre-eminent birth which is from the Most High Father, and also experienced that pre-eminent generation which is from the Virgin, the divine Scriptures do in both respects testify of Him: also, that He was a man without comeliness, and liable to suffering; that He sat upon the foal of an ass; that He received for drink, vinegar and gall; that He was despised among the people, and humbled Himself even to death and that He is the holy Lord, the Wonderful, the Counsellor, the Beautiful in appearance, and the Mighty God, coming on the clouds as the Judge of all men; — all these things did the Scriptures prophesy of Him.
3. For as He became man in order to undergo temptation, so also was He the Word that He might be glorified; the Word remaining quiescent, that He might be capable of being tempted, dishonoured, crucified, and of suffering death, but the human nature being swallowed up in it (the divine), when it conquered, and endured [without yielding], and performed acts of kindness, and rose again, and was received up [into heaven]. He therefore, the Son of God, our Lord, being the Word of the Father, and the Son of man, since He had a generation as to His human nature from Mary— who was descended from mankind, and who was herself a human being— was made the Son of man. Wherefore also the Lord Himself gave us a sign, in the depth below, and in the height above, which man did not ask for, because he never expected that a virgin could conceive, or that it was possible that one remaining a virgin could bring forth a son, and that what was thus born should be “God with us,” and descend to those things which are of the earth beneath, seeking the sheep which had perished, which was indeed His own peculiar handiwork, and ascend to the height above, offering and commending to His Father that human nature (hominem) which had been found, making in His own person the first-fruits of the resurrection of man; that, as the Head rose from the dead, so also the remaining part of the body— [namely, the body] of everyman who is found in life— when the time is fulfilled of that condemnation which existed by reason of disobedience, may arise, blended together and strengthened through means of joints and bands by the increase of God, each of the members having its own proper and fit position in the body. For there are many mansions in the Father's house, inasmuch as there are also many members in the body.
Source: Adversus haereses (New Advent)