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 family of David;
There is a possibility, at least, that under the circumstances they had decided to move to Bethlehem.  Some elements of the sacred accounts, such as their remaining in the area after Jesus' birth, "indicate that when Joseph and Mary went to Bethlehem, they were considering it a permanent move."[9] Harmonizing with this suggestion is the fact that after going to Egypt, they intended to return to "the land of Israel"; but upon learning that another Herod was on the throne, and in obedience to God's warning in a dream, they went instead to Galilee  (Matthew 2:21-23).  Summers pointed out that "Bethlehem was the historical headquarters of the stonemason's guild,"[10] an association that included "tektons" of at least three classes of workers.  These were carpenters, stonemasons, and certain kinds of farmers.  Luke omitted a number of events related by Matthew, not only because they were already well known from the "many" sources used by all the Gospels, but because they did not fit into the particular design of his Gospel.  Here, the big point is that the fulfillment of the prophecy of Christ's birth in Bethlehem was accomplished by the pagan lord of the empire, Augustus Caesar, whose census was the immediate cause of it.