This great work was indeed supremely worthy of the goodness of God. A king who has built a house or founded a city does not simply neglect it when robbers attack because of the inhabitants’ carelessness. He defends and saves it as his own work, looking not at the inhabitants’ neglect but at what is fitting for himself. Much more, then, the Word of the all-good Father did not neglect the human race, which had come into being through Him and was descending into corruption. By offering His own body, He abolished the death that had come upon them, and by His teaching He corrected their neglect. Thus by His own power He set right all that concerned humanity.
The Savior's own inspired disciples assure us of this. We read in one place: "For the love of Christ constrains 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 to ourselves, but to Him who died and rose again from the dead, even our Lord Jesus Christ." And again another says: "But we see Him who was made a little lower than the angels, even Jesus, crowned with glory and honor because of the suffering of death, so that by the grace of God He might taste death on behalf of everyone."
The same writer goes on to explain why it was necessary for God the Word and none other to become Man: "For it was fitting for Him, for whom are all things and through whom are all things, in bringing many sons to glory, to make the Author of their salvation perfect through suffering." He means that rescuing humanity from corruption belonged only to Him who made them in the beginning.
He also points out that the Word assumed a human body specifically so that He might offer it in sacrifice for bodies like His own: "Since then the children share in flesh and blood, He Himself likewise shared in the same, so that through death He might bring to nothing the one who has the power of death, that is to say, the Devil, and free those who all their lives were enslaved by the fear of death."
For by the sacrifice of His own body He brought the law against us to an end and gave us a new beginning of life and the hope of resurrection. Since death gained power over human beings through a human being, the destruction of death and the resurrection of life likewise came through the Incarnation of God the Word. As the man who bore Christ says, "For since death came through a human being, the resurrection of the dead also came through a human being. For just as all die in Adam, so all will be made alive in Christ," and what follows. We no longer die as those under condemnation, but as those who are to rise; we await the common resurrection of all, "which He will reveal at the proper times"—God, who accomplished it and graciously gave it to us.
This, then, is the first cause of the Savior’s Incarnation. From what follows, one may also understand that His gracious coming among us took place for good reason.