And also of the son of the bondwoman will I make {e} a nation, because he is thy seed.

(e) The Ishmaelites will come from him.

Wesley's Notes

21:13 The casting out of Ishmael was not his ruin. He shall be a nation because he is thy seed - We are not sure that it was his eternal ruin. It is presumption to say, that all these who are left out of the external dispensation of God's covenant are excluded from all his mercies. Those may be saved who are not thus honoured.

Jamieson-Fausset-Brown Bible Commentary

13. also of the son of the bondwoman will I make a nation-Thus Providence overruled a family brawl to give rise to two great and extraordinary peoples.

Matthew Henry's Concise Commentary

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.