Cast out this bondwoman and her son - Both Sarah and Abraham have been accused of cruelty in this transaction, because every word reads harsh to us. Cast out; גרש garash signifies not only to thrust out, drive away, and expel, but also to divorce; (see Leviticus 21:7); and it is in this latter sense the word should be understood here. The child of Abraham by Hagar might be considered as having a right at least to a part of the inheritance; and as it was sufficiently known to Sarah that God had designed that the succession should be established in the line of Isaac, she wished Abraham to divorce Hagar, or to perform some sort of legal act by which Ishmael might be excluded from all claim on the inheritance.

Wherefore she said unto Abraham, cast out this bondwoman and her son,.... Hagar, Sarah's handmaid and bondservant, and her son Ishmael; by this it appears that Hagar was concerned in this affair, and set her son on to mock Isaac, at least she encouraged him in it, buoying: him up with his being the firstborn, and having a right to the inheritance; wherefore Sarah saw plainly that there would be no peace nor comfort for her and her son, unless Hagar and her son were turned out of doors, for which she moves Abraham; and this not merely in a passion, but by divine direction and influence, as is evident from God's approbation of it:

for the son of this bondwoman shall not be heir with my son, even with Isaac; which he would seem to be, if continued, and would think himself so, and there would be continual bickerings about it; wherefore, to put it out of all doubt who was heir, she desires that he and his mother both might be cast out of the house, which would be a clear determination of this matter. Sarah may seem to take upon her too much, to be so peremptory, as to declare who should, and who should not be heir, which more properly belonged to Abraham, whom she called her lord, Genesis 18:12; but what will sufficiently free her from any charge of this kind is the revelation of the divine will, and the promise of God that so it should be; namely, that the covenant God had so often renewed with Abraham should be established with Isaac, and not with Ishmael, Genesis 17:19. Now what was the design of God, in guiding Sarah to make such a motion as this to Abraham, is taught us by the Apostle Paul, who makes these two women to be types and figures of the two covenants, and their sons of those that are under them, see Galatians 4:22.

Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, even with Isaac.

21:10 Cast out the bond - woman - This was a type of the rejection of the unbelieving Jews, who, though they were the seed of Abraham, yet, because they submitted not to the gospel - covenant, were unchurched and disfranchised. And that, which above any thing provoked God to cast them off, was, their mocking and persecuting the gospel - church, God's Isaac, in his infancy.

10. Wherefore she said unto Abraham, Cast out this bondwoman-Nothing but the expulsion of both could now preserve harmony in the household. Abraham's perplexity was relieved by an announcement of the divine will, which in everything, however painful to flesh and blood, all who fear God and are walking in His ways will, like him, promptly obey. This story, as the apostle tells us, in "an allegory" [Ga 4:24], and the "persecution" by the son of the Egyptian was the commencement of the four hundred years' affliction of Abraham's seed by the Egyptians.

21:9-13 Let us not overlook the manner in which this family matter instructs us not to rest in outward privileges, or in our own doings. And let us seek the blessings of the new covenant by faith in its Divine Surety. Ishmael's conduct was persecution, being done in profane contempt of the covenant and promise, and with malice against Isaac. God takes notice of what children say and do in their play; and will reckon with them, if they say or do amiss, though their parents do not. Mocking is a great sin, and very provoking to God. And the children of promise must expect to be mocked. Abraham was grieved that Ishmael should misbehave, and Sarah demand so severe a punishment. But God showed him that Isaac must be the father of the promised Seed; therefore, send Ishmael away, lest he corrupt the manners, or try to take the rights of Isaac. The covenant seed of Abraham must be a people by themselves, not mingled with those who were out of covenant: Sarah little thought of this; but God turned aright what she said.