Paul now returns to using Scripture to support his argument. He tells the story of two of Abraham's wives, Hagar and Sarah, and their children. He uses this story to show the difference between two types of people: those who are like slaves because they try to follow all the laws, and those who are free because they belong to Christ.
Paul uses a special way of explaining Bible stories (called allegory) that Jewish teachers used in those days (see study note on 4:24). Paul was trained as a rabbi (see Acts 22:3) and could effectively debate the Judaizers using their own methods.