And Sarah saw the son of Hagar. As the verb to laugh has a twofold signification among the Latins, so also the Hebrews use, both in a good and evil sense, the verb from which the participle mtschq (metsachaik) is derived. That it was not a childish and innoxious laughter, appears from the indignation of Sarah. It was, therefore a malignant expression of scorn, by which the forward youth manifested his contempt for his infant brother. And it is to be observed, that the epithet which is here applied to Ishmael, and the name Isaac, are both derived from the same root. Isaac was, to his father and others, the occasion of holy and lawful laughter; whence also, the name was divinely imposed upon him. Ishmael turns the blessing of God, from which such joy flowed, into ridicule. Therefore, as an impious mocker, he stands opposed to his brother Isaac. Both (so to speak) are the sons of laughter: but in a very different sense. Isaac brought laughter with him from his mother's womb, since he bore, -- engraven upon him, -- the certain token of God's grace. He therefore so exhilarates his father's house, that joy breaks forth in thanksgiving; but Ishmael, with canine and profane laughter, attempts to destroy that holy joy of faith. And there is no doubt that his manifest impiety against God, betrayed itself under this ridicule. He had reached an age at which he could not, by any means be ignorant of the promised favor, on account of which his father Abraham was transported with so great joy: and yet -- proudly confident in himself -- he insults, in the person of his brother, both God and his word, as well as the faith of Abraham. Wherefore it was not without cause that Sarah was so vehemently angry with him, that she commanded him to be driven into exile. For nothing is more grievous to a holy mind, than to see the grace of God exposed to ridicule. And this is the reason why Paul calls his laughter persecution; saying, He who was after the flesh persecuted the spiritual seed.' (Galatians 4:29.) Was it with sword or violence? Nay, but with the scorn of the virulent tongue, which does not injure the body, but pierces into the very soul. Moses might indeed have aggravated his crime by a multiplicity of words; but I think that he designedly spoke thus concisely, in order to render the petulance with which Ishmael ridicules the word of God the more detestable.

Mocking - What was implied in this mocking is not known. St. Paul, Galatians 4:29, calls it persecuting; but it is likely he meant no more than some species of ridicule used by Ishmael on the occasion, and probably with respect to the age of Sarah at Isaac's birth, and her previous barrenness. Jonathan ben Uzziel and the Jerusalem Targum represent Ishmael as performing some idolatrous rite on the occasion, and that this had given the offense to Sarah. Conjectures are as useless as they are endless. Whatever it was, it became the occasion of the expulsion of himself and mother. Several authors are of opinion that the Egyptian bondage of four hundred years, mentioned Genesis 15:13, commenced with this persecution of the righteous seed by the son of an Egyptian woman.

And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, (c) mocking.
(c) He derided God's promise made to Isaac which the apostle calls persecution (Galatians 4:29).

And Sarah saw the son of Hagar the Egyptian,.... That is, Ishmael, who is not expressed by name, but described by being a son of Hagar, a servant of Sarah's, and an Egyptian woman; all which seems to be observed by way of slight, both to Hagar and her son:
which she had born unto Abraham; not unto Sarah, as she proposed to herself, when she gave her maid to Abraham, Genesis 16:2. This son of Abraham she saw
mocking; either at the entertainment made at the weaning of Isaac; or rather at Isaac himself, laughing at his name, and treating him with contempt as his younger brother, and boasting that he was the firstborn, and that the inheritance belonged to him; and threatening what he would do to him, should he hereafter offer to dispute it with him, under pretence of the promise of God that he should be Abraham's heir, and at which promise also he may be supposed to mock: and that this contention was about the inheritance seems plain from the words of Sarah in Genesis 21:10; and in it Ishmael might not only rise to high words, but come to blows, and beat his brother; for it is observed the word used sometimes so signifies, 2-Samuel 2:14; wherefore the apostle might truly call it a persecution, Galatians 4:29; and as even cruel mockings are, Hebrews 11:35. As for the various senses the Jewish commentators put upon this, there does not seem to be any foundation for them, as that Ishmael was committing idolatry, and endeavouring to draw his brother into it; or was talking in an indecent and lascivious manner, in order to corrupt his mind; or that he was intending and attempting to take away his life, by shooting an arrow at him, and pretending it was but in jest and in play; See Gill on Galatians 4:29.

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.

Sarah saw the son of Hagar . . . mocking--Ishmael was aware of the great change in his prospects, and under the impulse of irritated or resentful feelings, in which he was probably joined by his mother, treated the young heir with derision and probably some violence (Galatians 4:29).

Sarah saw the son of the Egyptian mocking - Mocking Isaac no doubt, for it is sad, with reference to this, Galatians 4:29, that he that was born after the flesh, persecuted him that was born after the spirit. Ishmael is here called the son of the Egyptian, because (as some think) the four hundred years affliction of the seed of Abraham by the Egyptians began now, and was to be dated from hence.