Historians have been puzzled about the census. The one taken when Quirinius was governor of Syria. While all this begins to explain why Mary and Joseph were in Bethlehem, Luke is making a point. The birth of this little boy is the beginning of a confrontation between the kingdom of God - in all its apparent weakness, insignificance and vulnerability - and the kingdoms of the world. Caesar Agustus has never heard of Jesus of Nazareth. But within a century or so his successors in Rome had not only heard of him; they were taking steps to obliterate his followers. Within just over 3 centuries the Emperor himself became a Christian. When you see the manger on a card at Christmas, or in church, don't stop at the crib. See what it's pointing to. It's pointing to the explosive truth that the baby lying there is already being spoken of as the true King of the world. The rest of the story in Luke's gospel and later on in the Book of Acts will tell how he comes into his kingdom.
NT Wright. "Luke: For Everyone." Westminster John Knox Press: Kentucky. 2004. Page 21-22.