Luke 2:4

But in order that men might know that it was an enrolment of righteousness, there came up to it Joseph and Mary, the just man and the virgin. He who was to be guardian of the Word and she who was to bring it forth.

Now the registration of property was so appointed by Divine guidance, that every one was ordered to go into his own country, as it follows, And they all went to be taxed, every one to his own city. Which so came to pass, in order that the Lord, conceived in one place, born in another, might the more easily escape the fury of the crafty Herod. Hence it follows: Now Joseph also went up from Galilee.

Our city and country is the resting-place of the blessed, to which we ought to be travelling with daily increasing virtues. But day by day does Holy Church wait upon her Teacher, and going up from the course of worldly business (which the name of Galilee signifies) to the city of Judah, i. e. the city of confession and praise, make returns of her devotion to the Eternal King. She, after the example of the blessed Virgin Mary, a Virgin has conceived us of the Spirit. Though espoused to another, she is made fruitful by Him; and while visibly joined to the Pontiff who is placed over her, is invisibly filled with the graces of the Spirit. And hence Joseph is well interpreted increased, declaring by his very name, that the earnestness of the master speaking is of no avail, except he receive increasing help from above, that he may be heard.

(Irenæus cont. Hær. 1. 3. c. 11.) Now he added, a city of David, that he might declare that the promise made by God to David, namely, that from the fruit of his loins there should go before him a king for ever, (2 Sam. 7:12.) was already fulfilled. Whence it follows, Because he was of the house and lineage of David. (Ps. 132:11.) But since Joseph was of the family of David, it pleased the Evangelist to make known also that the Virgin herself was of the same family, because the Divine law enjoined marriages between those of the same line; and therefore it follows, With Mary his espoused wife.

(in diem natal. Christi.) It was the Lord who directed Augustus to give this edict, that he might minister unto the coming of the Only-begotten; for it was this edict that brought Christ's mother into her country as the prophets had foretold, namely, to Bethlehem of Judæa, according to the word, to a city of David, which is called Bethlehem.