At bottom, Christmas is a truth about God. Its initiative does not come from man. Briefly, it affirms that the world did not make itself to be what it is. Before the world, there was "I am." It turns out that the Godhead has its own proper inner life, complete in itself, and has no need for the world or us.
However, for His own purposes, God created the world, within which and for His purpose exists a central and free creature, the human being. This being is intended to participate in this inner life of God. God created a world in which He could be rejected by the free creature. He was, in fact, rejected.
God's response to this rejection was to send into the world His Son, the eternal Word, who was born of Mary in Bethlehem during the reign of Caesar Augustus. This incarnation, as it is called - this birth, life, and death of Christ - is the central event of human history and explains it. When we celebrate Christmas, this is what we celebrate: that Christ is true God and true man. Understanding this, everything else makes sense. Not understanding it, little else does.
Again, no link yet, so if you want to read it all now, buy the issue now.