And by your sword shall you live, and shall serve your brother; and it shall come to pass when you shall have the dominion, that you shall break his yoke from off your neck.
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Ambrose of Milan
This then is what the patriarch Isaac says, “You shall serve your brother. But the time will be, when you shall shake off and loose his yoke from your neck.” He means that there will be two peoples, one the son of the slave girl, the other of the free woman—for the letter is a slave, whereas grace is free—and that the people that attends to the letter is going to be a slave as long as it needs to follow the expounder of learning in the spirit. Then that will also come to pass which the apostle says, “that the remnant may be saved by reason of the election made by grace.” “You shall serve your brother,” but then you will perceive your advancement in servitude only when you begin to obey your brother voluntarily and not under compulsion. .
Everyone who does not possess the authority conferred by a clear conscience is a slave; whoever is crushed by fear or ensnared by pleasure or seduced by desires or provoked by wrath or felled by grief is a slave. In fact, every passion is servile, because “everyone who commits sin is a slave of sin,” and, what is worse, he is the slave of many sins. The person who is subject to vices has sold himself to many masters, so that he is scarcely permitted to go out of servitude. But take the one who is the master over his own will, judge over his counsels, agent of his judgment, the man who restrains the longing of his bodily passions and does well what he does. (Note that by acting well he acts rightly, and one who acts rightly acts without blame or reproach because he has power over his actions.) Such a person is assuredly free. For the one who does all things wisely and in complete accord with his will is the only free man. It is not accidental status that makes the slave but shameful and...
Nevertheless Esau brought it about by his demands and entreaties that he did receive a blessing but such a blessing as was in agreement and correspondence with the earlier one, namely, that he should serve his brother. Indeed, the one who could not command and rule the other ought to have served him, in order to be ruled by the one who was wiser. It was not the role of the holy patriarch to deliver his own son to the ignoble state of slavery. But since he had two sons, one without moderation and the other moderate and wise, in order to take care for both like a good father, he placed the moderate son over the immediate one, and he ordered the foolish one to obey the one who was wise. For the foolish man cannot of his own accord be a disciple of virtue or persevere in his intent, because the fool changes like the moon. Isaac was right to deny Esau freedom to make his own choices; else he might drift like a ship in the waves without a helmsman. But Isaac made him subject to his brother a...
Thy brother, in the reign of David, 2 Kings viii. 14, and of the Machabees. (Josephus, Antiquities xiii. 17.)
Yoke. When the house of Juda shall rebel against the Lord, in the days of Joram, then the Idumeans shall regain their liberty for a time; (4 Kings viii. 20.) to be subdued again after 800 years by John Hyrcan, the high priest. (Haydock)
All the blessing of Esau, tends to confirm that already given to his brother; so that the apostle seems to have considered it unworthy of notice. (Calmet)
Jacob, in the mean time, never asserted his dominion; but still called Esau his lord, (Chap. xxxii. 4.) and behaved to him with the greatest deference. (Haydock)
Yet the Idumeans always hated the Jews, and assisted Titus to destroy Jerusalem. (Josephus) (Tirinus)
And the words: “You shall live by your sword” mean that the people never stop being in defensive or aggressive war with the nations living around them, as Scripture itself shows. And the sentence “You shall be the servant of your brother” indicates the age that still continues, the age in which the Savior was present and came to visit his own brothers according to the flesh, and the Savior the prophet here suggests to serve after humanity has become obedient. That is why he said: “There will come a time when you shall shake and break the yoke from your neck.” Which yoke, but the yoke that lies in the law? Provided that they do not live any more as slaves under the yoke of the law but believe in the gospel as free men, they can still be saved.