Paul’s brief sketch of Israel’s history was designed to counter the arguments made by his opponents who claimed that they were the true descendants of Abraham and that Jerusalem—the center of Jewish Christianity and the law—was their mother. The Gentiles, they charged, were illegitimate; if they wanted to become true followers of Christ, they must first become a son of Abraham by submitting to the law of circumcision. 1
The truth, Paul says, is the opposite. These legalists are not the sons of Abraham but are illegitimate sons, like Ishmael. By placing their trust in circumcision, they were relying on “the flesh,” as Sarah did with Hagar and as the Israelites did with God’s law at Sinai. Gentile believers, however, were the sons of Abraham not by natural descent but, like Isaac, by the supernatural. “Like Isaac they were a fulfilment of the promise made to Abraham . . . ; like Isaac, their birth into freedom was the effect of divine grace; like Isaac, they belong to the column of the covenant of promise.”—James D. G. Dunn, The Epistle to the Galatians (London: Hendrickson Publishers, 1993), p. 256.
Being the promised child brought Isaac not only blessings but also opposition and persecution. In reference to persecution, Paul has in mind the ceremony in Genesis 21:8–10, where Isaac is being honored and Ishmael appears to make fun of him. The Hebrew word in Genesis 21:9 literally means “to laugh,” but Sarah’s reaction suggests Ishmael was mocking or ridiculing Isaac. While Ishmael’s behavior might not sound very significant to us today, it revealed the deeper hostilities involved in a situation when the family birthright was a stake. Many rulers in antiquity tried to secure their position by eliminating potential rivals, including siblings (Judg. 9:1–6). Although Isaac faced opposition, he also enjoyed all the privileges of love, protection, and favor that went along with being his father’s heir.
As spiritual descendants of Isaac, we should not be surprised when we suffer hardship and opposition, even from within the church family itself.
In what ways have you suffered persecution, especially from those closest to you, because of your faith? Or ask yourself this hard question: might you be guilty of persecuting others for their faith? Think about it.