Against the Heresies:
The reason the Word of God became man
from the treatise of Irenaeus, 130-200 A.D.
For this reason the Word of God became man and the Son of God became the son of man in order that man, being mingled with the Word of God and being granted adoption should become the son of God.
In no other way could we have received incorruptibility and immortality, without ourselves first being united to them. How could we be made one with incorruptibility and mortality by immortality and so enable us to receive adoption as sons.
This same Son of God, therefore, who is our Lord and the existing Word of the Father is also son of man. He was born like other men, born of Mary, who was herself of human stock and a member of the human race, and so he became the son of man.
It was for this reason that the Lord gave a sign here below and in heaven
above that man had not asked for. Man had neither hoped that a virgin
could be with child and bear a son, although she was a virgin; nor that
this child would be God with us, coming down to the earth below in search
of the sheep that was lost (which he himself had made) and once again ascending
on high and offering in trust to the Father the man he had found.
This same Lord himself became the first-fruits of the resurrection of man,
so that the resurrection of the head should mean the resurrection of the
rest of the body, and that every man alive should rise again on completion
of the time of the punishment, which his disobedience had earned.
For the body in its varied
joints and ligaments grows up and is strengthened by Godís aid, and each of the members has its appropriate fitting place in the body. The Father has many mansions in the same way as there are many members in the body.
When, therefore, man fell, God was geneours in mercy, since he foresaw the victory which would be his through the agency of the Word. For because his power was made perfect in weakness, he displayed the kindness of God and the greatness of his power.