Here Paul introduces his second illustration to emphasize the distinction between the 'justification by faith alone' gospel and the notion of works enabled salvation. Having introduced the picture of a guardian/child relationship, to represent the telos of the law, he now cites contrasts from the biography of Abraham's 2 sons: Isaac and Ishmael as an allegory of the true gospel vs. the Judaizer's heresy which was infecting Galatia. Sarah was the wife of promise. God had spoken that she would bear a son and thus fulfill God's prophecy to Abraham that he would be the father on many nations. However, Sarah was barren and the promise was slow to materialize, seemingly impossible through her. Jamieson, Faucet, and Brown comment: “After having sufficiently maintained his point by argument, the apostle confirms and illustrates it by an inspired allegorical exposition of historical facts, containing in them general laws and types. Perhaps his reason for using allegory was to confute the Judaizers with their own weapons... Paul meets them with an allegorical exposition – not the word of fancy - but sanctioned by the Holy Spirit. The history of the elect people, like their legal ordinances, had besides the literal, a typical meaning...”