Luke 2:4

Ver. 4-6. This was the occasion of Joseph's coming to Bethlehem, who either for fear of Herod, or for the convenience of his trade, (though he belonged to the tribe of Judah), was removed into Galilee; but he yieldeth obedience to the civil magistrates, and cometh to be enrolled in the court books belonging to the Roman empire, to which by this action he acknowledgeth himself a subject; he also by this act publicly declared both himself and Mary his wife to have been of the tribe of Judah, and of the family of David. We are told it was the custom of the Romans to enrol both women and children; however, Mary's personal attendance upon this homage might have been excused by her being great with child, had not the counsel of God so ordered it, that Christ should be born there; this doubtless carried Mary along with Joseph, he having now (according to the angel's direction, Matthew 1:20,24), took her unto him as his wife. While they were there, Mary's time of childbearing was accomplished: we have the like phrase Genesis 25:24.