This is a snippet out of the Book: “The Incarnation of the Word” from Athanasius, written in the fourth century. (Athanasius was a God fearing man, that fought for the trinity)
We saw in the last chapter that, because death and corruption were gaining ever firmer hold on them, the human race was in process of destruction. Man, who was created in God’s image and in his possession of reason reflected the very Word Himself, was disappearing, and the work of God was being undone. The law of death, which followed from the Transgression, prevailed upon us, and from it there was no escape. The thing that was happening was in truth both monstrous and unfitting. It would, of course, have been unthinkable that God should go back upon His word and that man, having transgressed, should not die; but it was equally monstrous that beings which once had shared the nature of the Word should perish and turn back again into non-existence through corruption. It was unworthy of the goodness of God that creatures made by Him should be brought to nothing through the deceit wrought upon man by the devil; and it was supremely unfitting that the work of God in mankind should disappear, either through their own negligence or through the deceit of evil spirits. As, then, the creatures whom He had created reasonable, like the Word, were in fact perishing, and such noble works were on the road to ruin, what then was God, being Good, to do? Was He to let corruption and death have their way with them? In that case, what was the use of having made them in the beginning? Surely it would have been better never to have been created at all than, having been created, to be neglected and perish; and, besides that, such indifference to the ruin of His own work before His very eyes would argue not goodness in God but limitation, and that far more than if He had never created men at all. It was impossible, therefore, that God should leave man to be carried off by corruption, because it would be unfitting and unworthy of Himself.
Yet, true though this is, it is not the whole matter. As we have already noted, it was unthinkable that God, the Father of Truth, should go back upon His word regarding death in order to ensure our continued existence. He could not falsify Himself; what, then, was God to do? Was He to demand repentance from men for their transgression? You might say that that was worthy of God, and argue further that, as through the Transgression they became subject to corruption, so through repentance they might return to incorruption again. But repentance would not guard the Divine consistency, for, if death did not hold dominion over men, God would still remain untrue. Nor does repentance recall men from what is according to their nature; all that it does is to make them cease from sinning. Had it been a case of a trespass only, and not of a subsequent corruption, repentance would have been well enough; but when once transgression had begun men came under the power of the corruption proper to their nature and were bereft of the grace which belonged to them as creatures in the Image of God. No, repentance could not meet the case. What–or rather Who was it that was needed for such grace and such recall as we required? Who, save the Word of God Himself, Who also in the beginning had made all things out of nothing? His part it was, and His alone, both to bring again the corruptible to incorruption and to maintain for the Father His consistency of character with all. For He alone, being Word of the Father and above all, was in consequence both able to recreate all, and worthy to suffer on behalf of all and to be an ambassador for all with the Father.
For this purpose, then, the incorporeal and incorruptible and immaterial Word of God entered our world. In one sense, indeed, He was not far from it before, for no part of creation had ever been without Him Who, while ever abiding in union with the Father, yet fills all things that are. But now He entered the world in a new way, stooping to our level in His love and Self-revealing to us. He saw the reasonable race, the race of men that, like Himself, expressed the Father’s Mind, wasting out of existence, and death reigning over all in corruption. He saw that corruption held us all the closer, because it was the penalty for the Transgression; He saw, too, how unthinkable it would be for the law to be repealed before it was fulfilled. He saw how unseemly it was that the very things of which He Himself was the Artificer should be disappearing. He saw how the surpassing wickedness of men was mounting up against them; He saw also their universal liability to death. All this He saw and, pitying our race, moved with compassion for our limitation, unable to endure that death should have the mastery, rather than that His creatures should perish and the work of His Father for us men come to nought, He took to Himself a body, a human body even as our own. Nor did He will merely to become embodied or merely to appear; had that been so, He could have revealed His divine majesty in some other and better way. No, He took our body, and not only so, but He took it directly from a spotless, stainless virgin, without the agency of human father–a pure body, untainted by intercourse with man. He, the Mighty One, the Artificer of all, Himself prepared this body in the virgin as a temple for Himself, and took it for His very own, as the instrument through which He was known and in which He dwelt. Thus, taking a body like our own, because all our bodies were liable to the corruption of death, He surrendered His body to death instead of all, and offered it to the Father. This He did out of sheer love for us, so that in His death all might die, and the law of death thereby be abolished because, having fulfilled in His body that for which it was appointed, it was thereafter voided of its power for men. This He did that He might turn again to incorruption men who had turned back to corruption, and make them alive through death by the appropriation of His body and by the grace of His resurrection. Thus He would make death to disappear from them as utterly as straw from fire.
The Word perceived that corruption could not be got rid of otherwise than through death; yet He Himself, as the Word, being immortal and the Father’s Son, was such as could not die. For this reason, therefore, He assumed a body capable of death, in order that it, through belonging to the Word Who is above all, might become in dying a sufficient exchange for all, and, itself remaining incorruptible through His indwelling, might thereafter put an end to corruption for all others as well, by the grace of the resurrection. It was by surrendering to death the body which He had taken, as an offering and sacrifice free from every stain, that He forthwith abolished death for His human brethren by the offering of the equivalent. For naturally, since the Word of God was above all, when He offered His own temple and bodily instrument as a substitute for the life of all, He fulfilled in death all that was required. Naturally also, through this union of the immortal Son of God with our human nature, all men were clothed with incorruption in the promise of the resurrection. For the solidarity of mankind is such that, by virtue of the Word’s indwelling in a single human body, the corruption which goes with death has lost its power over all. You know how it is when some great king enters a large city and dwells in one of its houses; because of his dwelling in that single house, the whole city is honored, and enemies and robbers cease to molest it. Even so is it with the King of all; He has come into our country and dwelt in one body amidst the many, and in consequence the designs of the enemy against mankind have been foiled and the corruption of death, which formerly held them in its power, has simply ceased to be. For the human race would have perished utterly had not the Lord and Savior of all, the Son of God, come among us to put an end to death.
The Word of God, by the offering of His own body He abolished the death which the human race had incurred, and corrected their neglect by His own teaching. Thus by His own power He restored the whole nature of man. The Savior’s own inspired disciples assure us of this. We read in one place:
“For the love of Christ constrainet us, because we thus judge that, if One died on behalf of all, then all died, and He died for all that we should no longer live unto ourselves, but unto Him who died and rose again from the dead, even our Lord Jesus Christ.”
[2 Cor. 5:14]
And again another says:
“But we behold Him Who hath been made a little lower than the angels, even Jesus, because of the suffering of death crowned with glory and honor, that by the grace of God He should taste of death on behalf of every man.”
The same writer goes on to point out why it was necessary for God the Word and none other to become Man:
“For it became Him, for Whom are all things and through Whom are all things, in bringing many sons unto glory, to make the Author of their salvation perfect through suffering.”
He means that the rescue of mankind from corruption was the proper part only of Him Who made them in the beginning. He points out also that the Word assumed a human body, expressly in order that He might offer it in sacrifice for other like bodies:
“Since then the children are sharers in flesh and blood, He also Himself assumed the same, in order that through death He might bring to nought Him that hath the power of death, that is to say, the Devil, and might rescue those who all their lives were enslaved by the fear of death.”
For by the sacrifice of His own body He did two things: He put an end to the law of death which barred our way; and He made a new beginning of life for us, by giving us the hope of resurrection. By man death has gained its power over men; by the Word made Man death has been destroyed and life raised up anew. That is what Paul says, that true servant of Christ:
“For since by man came death, by man came also the resurrection of the dead. Just as in Adam all die, even so in Christ shall all be made alive,”
[1 Cor. 15:21]
and so forth. Now, therefore, when we die we no longer do so as men condemned to death, but as those who are even now in process of rising we await the general resurrection of all,
“which in its own times He shall show,”
[1 Tim 6:15]
even God Who wrought it and bestowed it on us.
Full Document: http://www.ccel.org/ccel/athanasius/incarnation