Questions fill the air at Christmas: What’s on your list? Where is the party? What’s the greatest Christmas movie ever? (It’s a Wonderful Life.) What’s the worst? (A Christmas Story.)
But there’s another question that we should reflect upon during this season:
“Who do you say that I am?”
It’s a weighty and piercing question. Jesus posed it to the disciples in Matthew 16:15, and it is no less relevant today. For centuries, people have argued, debated, and persuaded others as to how to answer correctly. Nobody can phone-a-friend in an effort to recuse themselves from the implications. Throughout the year, but especially around Christmas, this question confronts us.
It was not so different a millennium and a half ago. Gregory of Nazianzus noted that a theological battle waged all around him in which his city was the arena. Bakers, bankers, and bartenders all argued about the nature of who Jesus was.  What was his relation to the father? How was he uniquely the God-man? Did he lose something or gain something when he came to Earth through the virgin Mary? These were all topics of conversation on the streets of the fourth and fifth centuries.
One voice rose to influence and prominence in these discussions: Leo the Great. Leo was adept at communicating the unity of the person of Christ while also maintaining a distinction between his divine and human natures. His sermon on Christmas day of 440 describes this well: “When, therefore, the identity of each substance is preserved and they join in a single Person, majesty takes up humility, strength takes up weakness, eternity takes up mortality . . . True God and true man are combined into the unity of the Lord.” 
His Christmas sermon two years later struck the same tone: “for the salvation of the world . . . true God was born, complete in divine attributes, complete in human ones. To recall us to eternal beatitude from our original chains and from worldly errors, he himself came down to us, he to whom we could not of ourselves rise up.” 
Recognizing the divinity and humanity of Christ was no exercise in mere speculation for Leo. Rather, it was an issue of eternal life and death. He understood that “we could not be released from the chains of eternal death had [Christ] not become lowly in our condition while remaining at the same time omnipotent in his own.” 
Leo’s Christological insights would play a significant role throughout the proceedings of the Council of Chalcedon in 451. His Tome, a letter written to Flavian of Constantinople in 449, was used a resource for the vocabulary of the Council’s eventual definition.
As we approach Christmas, let’s take after Leo. He recognized that thinking deeply about the person of Jesus is for all believers, not only the trained theologians. He thought it worthwhile to reflect upon the miracle of Christmas. God became man. Leo was constantly amazed that the voice through which the heavens were created also learned to laugh and hiccup and smile. The hands that hold the universe together had to learn to hold his mother’s finger. Those same hands would be pierced for the salvation of the world. Leo knew that to lose God as a man was to lose the doctrine of salvation.
You’ve got a lot to read this Christmas. Christmas lists. Christmas letters. Directions for your newest toy or gadget. But don’t neglect reading the Christmas story from Scripture. And, as a supplement, consider reading the definition of Chalcedon (also referred to as the Chalcedonian Creed). It drew upon Leo’s thought and has been read by believers for over 1500 years:
THEREFORE, following the holy fathers, we all with one accord teach men to acknowledge one and the same Son, our Lord Jesus Christ, at once complete in Godhead and complete in manhood, truly God and truly man, consisting also of a reasonable soul and body; of one substance with the Father as regards his Godhead, and at the same time of one substance with us as regards his manhood; like us in all respects, apart from sin; as regards his Godhead, begotten of the Father before the ages, but yet as regards his manhood begotten, for us men and for our salvation, of Mary the Virgin, the God-bearer; one and the same Christ, Son, Lord, Only-begotten, recognized in two natures, without confusion, without change, without division, without separation; the distinction of natures being in no way annulled by the union, but rather the characteristics of each nature being preserved and coming together to form one person and subsistence, not as parted or separated into two persons, but one and the same Son and Only-begotten God the Word, Lord Jesus Christ; even as the prophets from earliest times spoke of him, and our Lord Jesus Christ himself taught us, and the creed of the fathers has handed down to us.
“Who do you say that I am?” We say, along with Peter and the chorus of the saints throughout time, “You are the Christ, the Son of the living God.”
For God, who said “Let light shine out of darkness,” has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ.
– 2 Corinthians 4:6
 Christopher Dawson, The Making of Europe: An Introduction to the History of European Identity (Washington, D.C.: The Catholic University of America Press, 2003), 105.
 Jane Freeland and Agnes Conway, trans. St. Leo the Great: Sermons, vol. 93, The Fathers of the Church (Washington, D.C.: The Catholic University of America Press, 1996), 78.
 Ibid., 87-89.
 Ibid., 111.