4:21-27 The difference between believers who rested in Christ only, and those who trusted in the law, is explained by the histories of Isaac and Ishmael. These things are an allegory, wherein, beside the literal and historical sense of the words, the Spirit of God points out something further. Hagar and Sarah were apt emblems of the two different dispensations of the covenant. The heavenly Jerusalem, the true church from above, represented by Sarah, is in a state of freedom, and is the mother of all believers, who are born of the Holy Spirit. They were by regeneration and true faith, made a part of the true seed of Abraham, according to the promise made to him.
24. are an allegory—rather, "are allegorical," that is, have another besides the literal meaning.
these are the two covenants—"these [women] are (that is, mean; omit 'the' with all the oldest manuscripts) two covenants." As among the Jews the bondage of the mother determined that of the child, the children of the free covenant of promise, answering to Sarah, are free; the children of the legal covenant of bondage are not so.
one from—that is, taking his origin from Mount Sinai. Hence, it appears, he is treating of the moral law (Ga 3:19) chiefly (Heb 12:18). Paul was familiar with the district of Sinai in Arabia (Ga 1:17), having gone thither after his conversion. At the gloomy scene of the giving of the Law, he learned to appreciate, by contrast, the grace of the Gospel, and so to cast off all his past legal dependencies.
which gendereth—that is, bringing forth children unto bondage. Compare the phrase (Ac 3:25), "children of the covenant which God made … saying unto Abraham."
Agar—that is, Hagar.