John Calvin on Genesis 21:10

10. Cast out this bondwoman . Not only is Sarah exasperated against the transgressor, but she seems to act more imperiously towards her husband than was becoming in a modest wife. Peter shows, that when, on a previous occasion, she called Abraham lord, she did not do so feignedly; since he proposes her, as an example of voluntary subjection, to pious and chaste matrons. (1 Peter 3:6.) But now, she not only usurps the government of the house, by calling her husband to order, but commands him whom she ought to reverence, to be obedient to her will. Here, although I do not deny that Sarah, being moved by womanly feelings, exceeded the bounds of moderation, I yet do not doubt, both that her tongue and mind were governed by a secret impulse of the Spirit, and that this whole affair was directed by the providence of God. Without controversy, she was the minister of great and tremendous judgment. And Paul adduces this expression, not as a futile reproach, which an enraged woman had poured forth, but as a celestial oracle. But although she sustains a higher character than that of a private woman, yet she does not take from her husband his power; but makes him the lawful director of the ejection.