From a sermon by Gregory of Nazianzus, Bishop of Constantinople (389 AD)
Christ is born: glorify him. Christ comes from heaven: go out to meet him. Christ descends to earth: let us be raised on high. Let all the world sing to the Lord; let the heavens rejoice and let the earth be glad, for his sake who was first in heaven and then on earth. Christ is here in the flesh: let us exult with fear and joy – with fear, because of our sins; with joy, because of the hope that he brings us.
Once more the darkness is dispersed; once more the light is created. Let the people that sat in the darkness of ignorance now look upon the light of knowledge. The things of old have passed away; behold, all things are made new. He who has no mother in heaven is now born without father on earth. The laws of nature are overthrown, for the upper world must be filled with citizens. He who is without flesh becomes incarnate; the Word puts on a body; the Invisible is seen; he whom no hand can touch is handled; the Timeless has a beginning; the Son of God becomes Son of Man – Jesus Christ, the same yesterday, today and for ever.
Light from light, the Word of the Father comes to his own image, in the human race. For the sake of my flesh he takes flesh; for the sake of my soul he is united to a rational soul, purifying like by like. In every way he becomes human, except for sin. O strange conjunction! The Self-existent comes into being; the Uncreated is created. He shares in the poverty of my flesh, that I may share in the riches of his Godhead.
Source: Readings for the Daily Office from the Early Church, edited by Robert J. Wright (Church Publishing Inc., 1991), p. 34.