Galatians 4:29

Ishmael, the elder brother, persecuted him while still a nursing infant, claiming for himself the prior right of circumcision and the inheritance of the firstborn.… And it is aptly said that he who is born according to nature persecutes the spiritual. The spiritual one never persecutes the natural one but forgives him like an untutored brother, for he knows that he may progress.

— [THEODORET] Let this not trouble us either, that those entrusted are driven out by the unbelievers. For we find something of this kind also in the type, but it in no way prevailed against Isaac. [end of the excerpt by Theodoret] — "Yet as at that time." And from that very fact that the faithful were persecuted by the Jews (for they were then persecuted), he shows the pattern to be true. For even Ishmael, who was born according to the flesh, persecuted Isaac, who was born according to the Spirit and the promise. ...

What! does all this consolation consist in showing that freemen are persecuted by bond-men? By no means, he says, I do not stop here, listen to what follows, and then, if you be not pusillanimous under persecution, you will be sufficiently comforted. And what is it that follows? "Cast out the son of the handmaid, for he shall not inherit with the son of the freewoman." Behold the reward of tyranny for a season, and of recklessness out of season! the son is cast out of his father's house, and becomes, together with his mother, an exile and a wanderer. And consider too the wisdom of the remark; for he says not that he was cast forth merely because he persecuted, but that he should not be heir. For this punishment was not exacted from him on account of his temporary persecution, (for that would have been of little moment, and nothing to the point,) but he was not suffered to participate in the inheritance provided for the son. And this proves that, putting the persecution aside, this very thing had been typified from the beginning, and did not originate in the persecution, but in the purpose of God. Nor does he say, "the son of Abraham shall not be heir," but, "the son of the handmaid," distinguishing him by his inferior descent. Now Sarah was barren, and so is the Gentile Church; observe how the type is preserved in every particular, as the former, through all the by-gone years, conceived not, and in extreme old age became a mother, so the latter, when the fulness of time is come, brings forth. And this the prophets have proclaimed, saying, "Rejoice, thou barren that bearest not; break forth and cry, thou that travailest not; for more are the children of the desolate than of her which hath the husband." And hereby they intend the Church; for she knew not God, but as soon as she knew Him, she surpassed the fruitful synagogue.