In the following verses, Paul will argue that the law (Genesis) reveals that the son of the free woman is the one who gets to share in Abraham’s inheritance, not the son of the slave.1 He considers this interpretation to be one that the Galatians should have noticed for themselves in their study of Scripture. If they paid closer attention to Genesis, they would have realized that the promised inheritance comes through faith and not through imperfect works of obedience to the law. Paul can make this assumption because the particular passages from Genesis that he refers to were very familiar to the Jews (and Gentile converts). They were passages that stimulated a lot of discussion, debate, and speculation.2
21 Dites-moi, vous qui voulez être sous la loi, ne comprenez-vous point la loi?