4 But besides what we have said, there is another cause also, wherefore he has mentioned even this history; for to be sure, Zara's name was not cast at random on that of Phares. (For indeed it was irrelevant, and superfluous, when he had mentioned Phares, from whom he was to trace Christ's genealogy, to mention Zara also.) Wherefore then did he mention him? When Thamar was on the point of giving birth to them, the pangs having come upon her, Zara put forth his hand first. Then the midwife, when she saw this, in order that the first should be known, bound his hand with scarlet; but the child, when he was bound, drew in his hand, and when he had drawn it in, Phares came forth first, and then Zara. The midwife when she saw this said, “Why was the hedge broken up for you?”
Do you see the dark expression of mysteries? For it was not without purpose that these things were recorded for us: since neither was it worth our study to learn, what it might be that the midwife said; nor worth a narrative to know, that he who came out second, put forth his hand first. What then is the mysterious lesson? First, from the name of the child we learn what is inquired, for Phares is “a division,” and “a breach.” And moreover from the thing itself, which took place; for it was not in the order of nature that, having thrust out his hand, he should draw it in again when bound; these thing neither belonged to a movement directed by reason, nor did they take place in the way of natural consequence. For after the hand had found its way out, that another child should come forth before was perhaps not unnatural; but that he should draw it back, and give a passage for another, was no longer after the manner of children at the birth, but the grace of God was present with the children, ordering these things, and sketching out for us by them a sort of image of the things that were to come.
What then? Some of those who have examined these things accurately say, that these children are a type of the two nations. And so in order that you might learn that the polity of the latter people shone forth previously to the origin of the former, the child that has the hand stretched forth does not show itself entire, but draws even it in again; and after his brother had glided forth whole, then he too appears entire. And this took place also with regard to the two nations. I mean, that after the polity of the Church had been manifested in the times of Abraham, and then had been withdrawn in the midst of its course, the Jewish people came, and the legal polity, and then the new people appeared entire with their own laws. Wherefore also the midwife says, “Why was the hedge broken up for you?” because the law coming in had broken in upon the freedom of the polity. For indeed the Scripture is ever wont to call the law a hedge; as the prophet says: “You have broken down her hedge, so that all they which pass by the way do pluck off her grapes:” and, “I have set a hedge about it:” and Paul, “Having broken down the middle wall of the hedge.” But others say, that the saying, “Why was the hedge broken up for you?” was spoken touching the new people: for this at its coming put down the law.
Source: Homilies on the Gospel of St. Matthew (New Advent)