Keil & Delitzsch, Commentary on the Old Testament, [], Gen 21:8-21 Expulsion of Ishmael. - The weaning of the child, which was celebrated with a feast, furnished the outward occasion for this. Sarah saw Ishmael mocking, making ridicule on the occasion. "Isaac, the object of holy laughter, was made the butt of unholy wit or profane sport. He did not laugh (צחק), but he made fun (מצחק). The little helpless Isaac a father of nations! Unbelief, envy, pride of carnal superiority, were the causes of his conduct. Because he did not understand the sentiment, 'Is anything too wonderful for the Lord?' it seemed to him absurd to link so great a thing to one so small" (Hengstenberg). Paul calls this the persecution of him that was after the Spirit by him that was begotten after the flesh (Gal_4:29), and discerns in this a prediction of the persecution, which the Church of those who are born after the spirit of faith endures from those who are in bondage to the righteousness of the law.