But he who was of the bondwoman was born after the flesh; but he of the free woman was by promise.
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Augustine of Hippo
AD 430
Now the fact that Isaac was born of a free wife is not enough to make him signify the people who inherit the New Covenant. What is more important is that he was born according to the promise. For he could have been born according to nature’s norms from a slave and in the same way from a free woman, just as Abraham received from Katurah, whom he subsequently married, sons not according to a promise but according to nature.
He who was of the bondwoman. Ishmael was born according to the laws of natural generation, by which Abraham, though an old Prayer of Manasseh , was able to raise up seed from his youthful bondwoman, Hagar.
He of the freewoman was by promise. Isaac was not born according to the usual laws of generation, for Sarah, his mother, was then sterile by age, so that Abraham could not in the order of nature beget a son by her. He was born by promise, i.e, by the supernatural power of God, in fulfilment of the promise made to Abraham.
From God’s own Scripture it is evident that the birth of Ishmael also was according to promise. But the answer is that a promise is truly fulfilled in the giving of a covenant. It is one thing to bless, increase and multiply greatly, as is written in Ishmael’s case, but another to make an heir through a covenant. –.
Isaac was not born in the natural manner usual in marriages, or according to the body’s natural power, and yet was a lawful son…. Natural processes did not produce his conception, nor did the seed conceive him. For Sarah’s womb was dead both through age and through sterility. But the Word of God formed him…. Nevertheless the one not born according to the flesh was in greater honor than the one who was. Do not, then, be dismayed that you were not born according to the flesh, for your not being born according to the flesh makes you all the more kin to him. For conception that is not according to natural processes is more remarkable and more spiritual.
What is the meaning of after the flesh? Having said that Faith united us to Abraham, and it having seemed incredible to his hearers, that those who were not begotten by Abraham should be called his sons, he proves that this paradox had actually happened long ago; for that Isaac, born not according to the order of nature, nor the law of marriage, nor the power of the flesh, was yet truly his own son. He was the issue of bodies that were dead, and of a womb that was dead; his conception was not by the flesh, nor his birth by the seed, for the womb was dead both through age and barrenness, but the Word of God fashioned Him. Not so in the case of the bondman; He came by virtue of the laws of nature, and after the manner of marriage. Nevertheless, he that was not according to the flesh was more honorable than he that was born after the flesh. Therefore let it not disturb you that you are not born after the flesh; for from the very reason that you are not so born, are you most of all Abraham...
