The cave of Bethlehem resembles the cave of Hades into which Christ descends at His death. It also resembles the space framed by the rocks in most icons of Christ’s baptism. The same space can be seen on most icons of the crucifixion (beneath the cross and framing a skull). This iconographic similarity is not accidental. The cave of Bethlehem is meant to resemble the cave of Hades (just as the child in swaddling clothes resembles a body wrapped for burial). It resembles the cave of Hades for the same reason that the space framed by the rocks at Christ’s theophany resembles the cave of Hades. They are pointing to one and the same thing: Christ Incarnation is God’s descent into our world where sin and death reign. The incarnation of the Word is immediately a challenge to the darkness of death and hell.

St. John makes this clear in the prologue of his gospel. He speaks of Christ as the “Light of the world,” and within the same breath brings that Light into conflict with the darkness: “the Light shines in the darkness and the darkness has not overcome it.”

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Also from Fr. Stephen:
 

The same darkness marks the world to our day. The Light still shines and the darkness does not overcome it – but it is in darkness that the Light shines. The cave is the world – make no mistake.

Those who are baptized into Christ are baptized into His death according to St. Paul. It is also true that those who are baptized into Christ “receive the Light of Christ.” But to participate in the Light of Christ in this world is to be light in the midst of darkness.

I happened to see this example of a light in the darkness today. Please watch.