Note 2 at Gal. 4:22: Paul's statement, "it is written" refers to a summary of Genesis, chapters 16, 17 and 21. This is the story of Abraham's two sons, Isaac and Ishmael. Ishmael was born of a slave woman, while Isaac's mother, Sarah, was a free woman.

Note 3 at Gal. 4:22: Paul uses an allegory (v. 24) which is a type of interpretation common among the rabbis. An allegory interprets scriptural events or persons as foreshadowing a deeper spiritual truth. In this passage two women represent two covenants, and the two children represent a work of the flesh and a work of the Spirit.

The two women are Abraham's wives, Sarah and Hagar. Actually, Sarah was Abraham's wife and Hagar was an Egyptian slave who was the handmaiden of Sarah (Gen. 16:1). Sarah was barren so she suggested that Abraham have a sexual relationship with Hagar, and Sarah would raise the child as her own (Gen. 16:2). This was a common practice of their day.

Abraham did as Sarah wished, and Hagar had a child named Ishmael (Gen. 16:4, 11). However, God made it clear that this was not the child He had promised to Abraham through whom God would fulfill His promise (Gen. 17:20-21). So, approximately 14 years after the birth of Ishmael (see note 2 at Rom. 4:10, p. 763), Abraham and Sarah had a child supernaturally, who was named Isaac (Gen. 21:1-3).

Ishmael, the son of Hagar, persecuted Isaac, the son of Sarah, to the degree that Sarah begged Abraham to send Hagar and her son Ishmael away (Gen. 21:9-10). Abraham did not want to do this, but God spoke to him and told him to do as Sarah had said (Gen. 21:11-12).

Paul now interprets the significance of these actions. Ishmael was a product of self effort, just as any trust in the law for the purpose of justification would be. In contrast, Isaac was supernatural. Both Abraham and Sarah were well beyond the age of having children, so Isaac was a miracle. Likewise, salvation by grace is a miracle, not self effort.

In the same way that Hagar and her son, who was a product of the flesh, were cast out, so those who seek to be justified by the law are rejected by God. But those who believe the gospel and receive salvation as a gift are like Isaac, who came supernaturally through the promise of God.

Thus Paul shows that the truths of the gospel were present in the Old Testament law (see note 3 at Rom. 1:2, p. 740), but the legalistic Jews had been blinded to these simple truths. They had misinterpreted the purpose of the Old Testament law (see note 4 at Rom. 3:19, p. 757) and were therefore wrongfully teaching that conformity to the law was necessary for salvation. Peter spoke of people who were willfully ignorant of the truth (2 Pet. 3:5). Paul said in Galatians 3:1 that legalism is crazy (see note 1 at Gal. 3:1, p. 1064)