St. Peter Chrysologus on the Reason for the Incarnation of God

The Word was made Incarnate to restore the nature of mankind.

He has made you in his image that you might in your person make the invisible Creator present on earth; he has made you his legate, so that the vast empire of the world might have the Lordʼs representative. Then in his mercy God assumed what he made in you; he wanted now to be truly manifest in man, just as he had wished to be revealed in man as in an image. Now he would be in reality what he had submitted to be in symbol. And so Christ is born that by his birth he might restore our nature. He became a child, was fed, and grew that he might inaugurate the one perfect age to remain for ever as he created it. He supports man that man might no longer fall. And the creature he had formed of earth he now makes heavenly; and what he had endowed with a human soul he now vivifies to become a heavenly spirit. In this way he fully raised man to God, and left in him neither sin, nor death, nor travail, nor pain, nor anything earthly, with the grace of our Lord Christ Jesus, who lives and reigns with the Father in the unity of the Holy Spirit, now and for ever, for all the ages of eternity. 

Rejoice!  The Lord has Come.

Reference: The Sacrament of Christʼs Incarnation by St. Peter Chrysologus