We sing joy to the world at Christmas, says Spurgeon, “because it is evermore a joyous fact that God should be in alliance with man, especially when the alliance is so near that God should in very deed take our manhood into union with his godhead; so that God and man should constitute one divine, mysterious person” (see “Joy Born at Bethlehem”).
This is what Christians mean when we speak of the Incarnation: the joining together of God and man in “one divine, mysterious person,” the Lord Jesus Christ.
The Incarnation is an especially joyful and important doctrine for Christians because, not only did God align with man, but through this alignment Jesus gained a human body that could in turn be sacrificed to endure God’s wrath. This was the only way that man could be saved. As Spurgeon explains,
Sin had separated between God and man; but the incarnation bridges the separation: it is a prelude to the atoning sacrifice, but it is a prelude full of the richest hope. From henceforth, when God looks upon man, he will remember that his own Son is a man. From this day forth, when he beholds the sinner, if his wrath should burn, he will remember that his own Son, as man, stood in the sinner’s place, and bore the sinner’s doom.
When we understand the purpose for which Jesus was incarnated, we can bring a much greater depth to our Christmas singing. We can sing carols like “Hark! The Herald Angels Sing” with newfound wonder and worship as we consider the nature of the newborn Jesus, and the purpose for which he came:
Veiled in flesh the Godhead see; Hail th’incarnate Deity, Pleased as man with men to dwell, Jesus our Immanuel…
Mild he lays his glory by, born that man no more may die, born to raise the sons of earth, born to give us second birth. Hark! the herald angels sing, “Glory to the new born King!”