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God assumed the whole of humanity in His Incarnation

Wherefore Luke points out that the pedigree which traces the generation of our Lord back to Adam contains seventy-two generations, connecting the end with the beginning, and implying that it is He who has summed up in Himself all nations dispersed from Adam downwards, and all languages and generations of men,  together with Adam himself. Hence also was Adam himself termed by Paul "the figure of Him that was to come,"

IRENAEUS AGAINST HERESIES -- BOOK III CHAP. XXI, 3
For He would not have been one truly possessing flesh and blood, by which He redeemed  us, unless He had summed up in Himself the ancient formation of Adam.
IRENAEUS AGAINST HERESIES -- BOOK V  CHAP. I, 2
 
For by summing up in Himself the whole human race from the beginning to the end, He has also summed up its death. 
IRENAEUS AGAINST HERESIES -- BOOK V  CHAP. XXIII 2
 
God recapitulated in Himself the ancient formation of man, that He might kill sin, deprive death of its power, and vivify man.
IRENAEUS AGAINST HERESIES -- BOOK III Chap. XVIII 7
 
This, therefore, the Word of God was made, recapitulating in Himself His own handiwork; and on this account does He confess Himself the Son of man
IRENAEUS AGAINST HERESIES -- BOOK III Chap. XXII 1
 
In like manner, too, did the Lord say to those who should afterwards shed His blood, "All righteous blood shall be required which is shed upon the earth, from the blood of righteous Abel to the blood of Zacharias the son of Barachias, whom ye slew between the temple and the altar. Verily I say unto you, All these things shall come upon this generation."(7) He thus points out the recapitulation that should take place in his own person of the effusion of blood from the beginning, of all the righteous men and of the prophets, and that by means of Himself there should be a requisition of their blood. Now this [blood] could not be required unless it also had the capability of being saved; nor would the Lord have summed up these things in Himself, unless He had Himself been made flesh and blood after the way of the original formation [of man], saving in his own person at the end that which had in the beginning perished in Adam.
IRENAEUS AGAINST HERESIES -- BOOK V  CHAP. XIV 1
 
For the Lord, taking dust from the earth, moulded man; and it was upon his behalf that all the dispensation of the Lord's advent took place. He had Himself, therefore, flesh and blood, recapitulating in Himself not a certain other, but that original handiwork of the Father, seeking out that thing which had perished. 
IRENAEUS AGAINST HERESIES -- BOOK V  CHAP. XIV 2
 
Part II
 
But profitably does he affirm that the Word dwelt in us, unveiling to us this deep Mystery also: for we were all in Christ, and the community of human nature mounteth up unto His Person; since therefore was He named the last Adam,, giving richly to the common nature all things that belong to joy and glory, even as the first Adam what pertained to corruption and dejection. ... in order that having all in Himself, He might reconcile all in one body unto the Father, as Paul saith.
St. Cyril: Commentary on the Gospel of St. John Book 1 pg 111 (65)
 
For all we were in Christ, Who on account of us and for us died and rose again. 
St. Cyril: Commentary on the Gospel of St. John Book 2 pg 132 (2)
 
For the whole human nature was in Christ, in that He was Man.... He, having been made Man, had our whole nature in Himself, that He might uplift it all transfashioning it unto its olden state.
St. Cyril: Commentary on the Gospel of St. John Book 5 pg 548 (22)
 
Therefore the Word of God made one with Himself human nature in its entirety, that so He might save the entire man. For that which has not been taken into His Nature, has not been saved.
St. Cyril: Commentary on the Gospel of St. John Book 8 pg 152 (9)
 
He is still one of us as He sits at the right hand of God the Father, ... He has presented Himself therefore as Man to the Father on our behalf, that so He may restore us, who had been removed from the Father's presence by the ancient transgression.
St. Cyril: Commentary on the Gospel of St. John Book 9 pg 236 (40-41)
 
For in Him we all have our being, inasmuch as He manifested Himself as Man. ... It was necessary then to confer on the nature of man the height of blessedness, and not only to rid it of death and sin, but to raise it even to the heavens themselves, and to make man a companion of the angels, and a partaker in their joys. And just as by His own Resurrection He renewed in us the power of escaping corruption, even so He thought it right to open out for us the path heavenwards, and to set in the Presence of the Father the race of man who had been cast out of His sight owing to Adam's transgression. ... There, as Man, ... He sits on His own Father's throne, and even on us too will the glory thereof be reflected. For this reason also Paul said concerning the Father: And He raised us up with Him, and made us to sit with Him in the heavenly places in Christ. 
St. Cyril: Commentary on the Gospel of St. John Book 10 pg 442 (67)
 
For so being Rich, became He poor, bringing us again unto His own wealth and having all in Himself through the flesh which was united to Him. For thus have we been buried with Christ through Holy Baptism, have been raised and made to sit with Him in heavenly places.  
St. Cyril: 5 Tomes against Nestorius book 1 pg 4
 
A personal note: It is sad that the late Hegoumen Matta Al Maskeen of blessed memory was slandered because he alluded to this important patristic doctrine in his writings.