The lead-up to Christmas was the first time I ever experienced “sehnsucht”—the inconsolable longing not satisfied by anything in this world. I remember the music (especially the minor key stuff), the lights on the tree, the cooling weather (a welcome reprieve in Florida) and the smell of mom’s candles combining to charge the air in our home with expectation. Like good Baptists, we didn’t consciously celebrate Advent, but by Dickens, we kept it in our hearts.

Even at that young age, I understood that what I longed for—what I hoped for—wasn’t in the music, the decorations, the food, or even the plastic dinosaurs wrapped beneath the tree. The object of my desire was in the manger, pictured by a ceramic stand-in whose visitation triggered awe, sadness, and an electrifying sense that a Grand Miracle had taken place.

Years later I learned that for the medieval Church, Advent and Christmas weren’t that big of a deal. Lent and Easter dominated the liturgical calendar, marking the Lord’s triumph over sin and death and mirroring the emphasis of the New Testament. Even so, the rise in prominence of Christ’s birth in worship and imagination seem right to me.

The Resurrection only makes sense in light of the Incarnation. In many ways, the miracle of Christ’s return from the grave is the fulfillment of a promise made by His Incarnation. Having joined Himself inseparably with creation, God the Son could no sooner surrender this world to decay than He could suffer decay, Himself. The Resurrection had to happen, precisely because the Incarnation could not be reversed.

In his appropriately titled “Miracles,” C. S. Lewis calls God donning humanity in Mary’s womb “the Grand Miracle,” and “the central event in the history of the Earth—the very thing that the whole story has been about.” When you understand his atonement theology, remarks like this make sense. Lewis drew heavily on the fourth-century theologian Athanasius, even writing a preface to the Church Father’s masterpiece, “On the Incarnation.” Athanasian themes loom large in “The Perfect Penitent,” the section of “Mere Christianity” in which Lewis unpacks the meaning of Christ’s Incarnation and Passion.

According to Lewis, human beings had gotten ourselves in a pickle with God. And as the responsible party, it fell to human beings to set things right. We would have to pay our debt, which meant repenting perfectly, dying to self, and returning to God. But there was a problem: “…the same badness which makes us need [repentance], makes us unable to do it.” The very sin that places us in God’s debt makes us incapable of paying that debt. We would need God’s help in order to “surrender, to suffer, to submit, to die.” But God, in His own nature, never does such things! Indeed, if the classical theists are correct, God cannot move at all from potency to act. He cannot change. It turns out that “the one road for which we now need God’s leadership most of all is a road God, in His own nature, has never walked.”

“But,” Lewis adds (I imagine after a pregnant pause in the original radio address) “…supposing God became a man.” Such a Person—possessed of the inexhaustible power and holiness of Divinity but clothed in the flesh, blood, and rational animal nature of man—could suffer, submit, change, and die, and do all of these perfectly. As man He could discharge man’s debt by living the life God required and dying the death justice demanded. But as God, He could elevate human nature to something hitherto unimagined: “For He was made man that we might be made God,” writes Athanasius, “and He

manifested Himself by a body that we might receive the idea of the unseen Father; and He endured the insolence of men that we might inherit immortality.”

From this we get a sense of what Lewis means by calling the Incarnation “the Grand Miracle”—the very fulcrum of history. In becoming a man, the Word bridged not only the abyss between holiness and sin but the infinity between Creator and creature. In Jesus, God permanently joined Himself with creation, becoming a creature Himself, united forever with our race as a Kinsman Redeemer, which is Old-Testament-speak for our rich big Brother.

We also get a sense of why the hope and desire of Advent are mingled with sadness. Between the manger and the empty tomb is a horrible cross. We rightly mourn for our Brother as He volunteers his newly-birthed flesh to be torn on our behalf. Yet volunteer it He must. This was, after all, His central reason for becoming human—that by inhabiting a body subject to death, He could exhaust the power of death and destroy the grave from the inside.

In Hebrews 2:14-17, the Incarnation is the miracle that prepares God to stand in our place and die in our stead. His human body and soul give Him the legal and natural right to serve as our substitute: “Since therefore the children share in flesh and blood, he himself likewise partook of the same things, that through death he might destroy the one who has the power of death, that is, the devil, and deliver all those who through fear of death were subject to lifelong slavery. Therefore he had to be made like his brothers in every respect, so that he might become a merciful and faithful high priest in the service of God, to make propitiation for the sins of the people.”

Athanasius strengthens the substitutionary element, here, writing: “…thus taking from our bodies one of like nature, because all were under the penalty of corruption of death, He gave it over to death in the stead of all, and offered it to the Father,” in order that “all being held to have died in Him, the law involving the ruin of men might be undone,” and “He might turn them again toward incorruption, and quicken them from death by the appropriation of His body and by the grace of the Resurrection, banishing death from them like straw from the fire.”

In the Incarnation, all our hopes and fears meet, as the carol has it. The solemn joy that sparked longing in my young imagination is a fitting reaction to history’s central event. Far from diminishing Easter, our anticipation of the Grand Miracle of God becoming human during Advent deepens our understanding of Jesus’ identity and sharpens our longing both for His Resurrection and ours. This fast and the feast to follow give us confidence that Christ’s triumph over sin and death will be our triumph, because it reminds us every year that we hope and believe in a God who is not only for us, but also with us.