Paul uses the story of Hagar and Sarah in 4:21–27 to explain the situation in Galatia. Isaac represents those born through God's promise (see 3:8) by the Spirit's power (3:2–5; see also Ephesians 1:13–14). These people trust in God for salvation through Christ by faith. Ishmael represents those who think following the law of Moses will make them acceptable to God (Galatians 3:10–11). This idea would have surprised the Judaizers, who believed they were Abraham's true children because they followed the law of Moses.