Galatians 4:22

It is written in the law, that is, in Genesis, (chap. xvi. and chap. xxi.) that Abraham had two sons, &c. that his two sons, Ismael, born of his servant, Agar, and Isaac of his wife, Sara, in an allegorical sense, represent the two testaments or covenants, which God made with his people: that by Ismael was represented that covenant of the former law delivered to Moses on Mount Sina, by which the Jews were made his elect people, yet as it were his servants, to be kept to their duty by fear of punishments; but by Isaac is represented the new covenant or testament of Christ, given at Jerusalem, where he suffered, where the new law was first published; by which law, they who believe in Christ were made the spiritual children of Abraham, the sons of God, and heirs of the blessings promised to Abraham: that Sina, the mountain in Arabia, hath[3] an affinity with Jerusalem, and with here children, who remain under the servitude of the law of Moses: we cannot understand a conjunction, or an affinity, as to place and situation, Sina and Jerusalem being nearly twenty days' journey distant from each other; therefore it can only be an affinity in a mystical signification, inasmuch as Jerusalem was the capital of the Jews, where the children of those who received the law on Mount Sina lived still under the servitude of the same law: but Christians, who believe in Christ, must look upon themselves as belonging to Jerusalem, and not to the city of Jerusalem upon earth, but to the celestial Jerusalem in heaven, which is our mother, now no longer servants and slaves to the former law, but free, being made the sons of God by the grace of Christ, and heirs of heaven. And these blessings were promised to all nations, not only to the Jews, of which the much greater part remained obstinate, and refused to believe in Christ, but also particularly to the Gentiles, according to the prophecy of Isaias, (chap. liv.) rejoice thou that hast been barren, like Sara, for a long time; i.e. rejoice, you Gentiles, hitherto left in idolatry, without knowledge or worship of the true God, now you shall have more children among you than among the Jews, who were his chosen people. (Witham)