Genesis 21:8

8. And the child grew, and was weaned. Moses now begins to relate the manner in which Ishmael was rejected from the family of Abraham, in order that Isaac alone might hold the place of the lawful son and heir. It seems, indeed, at first sight, something frivolous, that Sarah, being angry about a mere nothing, should have stirred up strife in the family. But Paul teaches, that a sublime mystery is here proposed to us, concerning the perpetual state of the Church. (Galatians 4:21.) And, truly, if we attentively consider the persons mentioned, we shall regard it as no trivial affair, that the father of all the faithful is divinely commanded to eject his firstborn son; that Ishmael, although a partaker of the same circumcision, becomes so transformed into a strange nations as to be no more reckoned among the blessed seed; that, in appearance, the body of the Church is so rent asunder, that only one-half of it remains; that Sarah, in expelling the son of her handmaid from the house, claims the entire inheritance for Isaac alone. Wherefore, if due attention be applied in the reading of this history, the very mystery of which Paul treats, spontaneously presents itself.

And Abraham made a great feast. It is asked, why he did not rather make it on the day of Isaac’s birth, or circumcision? The subtile reasoning of Augustine, that the day of Isaac’s weaning was celebrated, in order that we may learn, from his example, no more to be children in understandings is too constrained. What others say, has no greater consistency; namely, that Abraham took a day which was not then in common use, in order that he might not imitate the manners of the Gentiles. Indeed, it is very possible, that he may also have celebrated the birthday of his son, with honor and joy. But special mention is made of this feast, for another reason; namely, that then, the mocking of Ishmael was discovered. For I do not assent to the conjecture of those who think that a new history is here begun; and that Sarah daily contended with this annoyance, until, at length, she purged the house by the ejection of the impious mocker. It is indeed probable, that, on other days also, Ishmael had been elated by similar petulance; yet I do not doubt but Moses expressly declares that his contempt was manifested towards Sarah, at that solemn assembly, and that from that time, it was publicly proclaimed. Now Moses does not speak disparagingly of the pleasures of that feast, but rather takes their lawfulness for granted. For it is not his design to prohibit holy men from inviting their friends, to a common participation of enjoyment, so that they, jointly giving thanks to God, may feast with greater hilarity than usual. Temperance and sobriety are indeed always to be observed; and care must be taken, both that the provision itself be frugal, and the guests moderate. I would only say, that God does not deal so austerely with us, as not to allow us, sometimes, to entertain our friends liberally; as when nuptials are to be celebrated, or when children are born to us. Abraham, therefore, made a great feast, that is, an extraordinary one; because he was not accustomed thus sumptuously to furnish his table every day; yet this was an abundance which by no means degenerated into luxury. Besides, while he was thus liberal in entertaining his friends according to his power, he also had sufficient for unknown guests, as we have seen before.