The second week of Advent in our church year always features a gospel reading focusing on John the Baptist. Luke portrays John the Baptist very clearly to the readers of his time as fitting into the mold of an Old Testament prophet. Prophets of the Hebrew Traditions frequently spoke out against ruling authorities and political systems as agents of oppression, and in a similar way, John the Baptist points to a complete change of the power structure of his time. This means that Christmas, for us, is more than a celebration of a theological mystery (although it is that) – it's a surprisingly subversive act.
(In other words, hang an ornament, stick it to the Man.)