BECAUSE the Christmas story has been told so often for so long, it’s easy even for Christians to forget how revolutionary Jesus’ birth was. The idea that God would become human and dwell among us, in circumstances both humble and humiliating, shattered previous assumptions. It was through this story of divine enfleshment that much of our humanistic tradition was born.

For most Christians, the incarnation — the belief that God, in the person of Jesus, walked in our midst — is history’s hinge point. The incarnation’s most common theological take-away relates to the doctrine of redemption: the belief that salvation is made possible by the sinless life and atoning death of Jesus. But there are other, less familiar aspects of Jesus’ earthly pilgrimage that are profoundly important.

One of them was rejecting the Platonic belief that the material world was evil. In Plato’s dualism, there was a dramatic disjuncture between ideal forms and actual bodies, between the physical and the spiritual worlds. According to Plato, what we perceive with our senses is illusory, a distorted shadow of reality. Hence philosophy’s most famous imagery — Plato’s shadow on the cave — where those in the cave mistook the shadows for real people and named them.

This Platonic view had considerable influence in the early church, but that influence faded because it was in tension with Christianity’s deepest teachings. In the Hebrew Bible, for example, God declares creation to be good — and Jesus, having entered the world, ratified that judgment. The incarnation attests to the existence of the physical, material world. Our life experiences are real, not shadows. The incarnation affirms the delight we take in earthly beauty and our obligation to care for God’s creation. This was a dramatic overturning of ancient thought.