Merry Christmas to all! Last Tuesday, the LDS & Evangelical Conversations blog ran a post titled "Christ Came Down", which merely quoted from the Definition of Chalcedon, the essential historic Christian statement (from the Council of Chalcedon in the year 451) about the hypostatic union - that is, the facet of the Incarnation that means that Christ is one personal substance uniting in harmony two fundamental natures, deity and humanity. The comments on this post, from a variety of perspectives, explored the ways that Latter-day Saints and traditional Christians use the word "Incarnation" somewhat differently, and thus understand the significance of Christmas differently.
Christmas doesn't seem to be a suitable time for debate, so I won't comment extensively on what seems to be the crux of the classic LDS perspective on the Incarnation. I'll simply say that the significance of Christmas as a holy day of remembrance seems, in the classic LDS view, to derive particularly from two points of differentiation between the birth of Jesus and the births of the rest of us: (1) Although all persons of the divine/human species must inevitably enter into a mortal realm to gain a physical body, Jesus is distinguished from us because he had already earned Godhood before doing so, and thus came to earth as a God rather than to become a God; and (2) Whereas most of us receive our earthly body through the contributions of a mortal mother and mortal father, Jesus received his earthly body through the contributions of a mortal mother and an immortal Father, thus inheriting even in his bodily capacities some traits from each.
The traditional Christian perspective on the Incarnation is much different than this. (Personally, I find it significantly more beautiful and awe-inspiring.) The traditional Christian view is predicated on numerous background assumptions about the Creator/creation dichotomy. Only God is eternal, necessary, and transcendent; all other things are temporal and contingent. There is an immense difference between God and all other realities. All these other realities, which together can be collectively labeled 'creation', resulted from the freely chosen activity of God and continue to exist because of the continued freely chosen activity of God. They stand in a unilateral relationship of dependence. God is sui generis: there can be only one example of what it means to be God, and he is that example. Nothing that is God can cease to be God; nothing that is not God can become God. (Nevertheless, God is internally plural, being eternally and necessarily expressed tripersonally: as Father, Son, and Holy Spirit. It is these eternal relationships that establish Christ's divine Sonship, and not the circumstances of his earthly birth, which really were truly virginal.) The divine nature, or 'deity', is what it means to be God in this sense. This divine nature is set over against the natures of all created kinds, including human nature, or 'humanity'.
The Incarnation is the mind-blowing event wherein, quite paradoxically but no less true for the paradox, a person who is God (that is, who shares in the unique divine nature of 'deity') also becomes a person who is human (that is, who shares in the human nature, or 'humanity'), without ceasing to be God. Thus, the Definition of Chalcedon makes clear that we have a single person who fully exemplifies two natures, one uncreated and one created: "the same one, perfect in deity and also perfect in humanity, truly God and truly human", being "one and the same Christ, Son, Lord, only-begotten, to be acknowledged in two natures, inconfusedly, unchangeably, indivisibly, inseparably", with "the property of each nature being preserved, and concurring in one Person and Subsistence". The Creator breaks into creation; the Creator unites a created reality to his very self. The entire structure of reality is permanently changed by this occurrence in and of itself. The implications defy domestication, but cries out to let the paradox (not a contradiction, but indeed a paradox) highlight the love of God, as we see in, for instance, this Christmas hymn by Charles Wesley:
Let angels and archangels sing
The wonderful Immanuel's Name,
Adore with us our newborn King,
And still the joyful news proclaim:
All heaven and earth be ever joined,
The praise the Savior of mankind.
The everlasting God comes down
To sojourn with the sons of men;
Without his majesty or crown,
The great Invisible is seen;
Of all his dazzling glories shorn,
The everlasting Word is born!
Angels, behold that Infant's face,
With rapturous awe the Godhead own,
'Tis all your heaven on him to gaze,
And cast your crowns before his throne;
Tho' now he on his footstool lies,
Ye know he built both earth and skies.
By him into existence brought,
Ye sang the all-creating Word;
Ye heard him call our world from nought,
Again, in honor of your Lord,
Ye morning stars, your hymns employ,
And shout, ye sons of God, for joy.
Glory be to Christ! Merry Christmas!