As often before, Bruegel treats a biblical story as a contemporary event. And once again, reference to particular political events has been adduced - in this case, the severity of the Spanish administration in the southern Netherlands. However, Bruegel may well be making a more general criticism of bureaucratic methods.
And it came to pass in those days that a decree went out from Caesar Augustus that all the world should be registered... So all went to be registered, everyone to his own city. Joseph also went up from Galilee, out of the city of Nazareth, into Judea, to the city of David, which is called Bethlehem, because he was of the house and lineage of David, to be registered with Mary, his betrothed wife, who was with child.