And you brethren, like Isaac, are children of promise.Galatians 4:28(NASB)
Paul wrote his epistle to the Galatians in order to help the Judaisers and the legalists of his day, understand the difference between the freedom we have in Christ.. and the restrictive bondage to sin, which comes from the Law. Paul aims to differentiate between believers, who are set free from bondage to the Law by faith in Christ.. and those who are legalistic, and remain enslaved to sin, and bound.. by works of the flesh to the Mosaic Law.
He wanted to demonstrate the great gulf that there is between the freedom we receive, by grace through faith in Christ, and the stifling subjugation that comes from trying to keep the Law. He desires to ward us against following another 'gospel' and a different 'Jesus'.
Paul took the historic figures of Isaac and Ishmael, the two sons of the great patriarch Abraham, and used these two characters to illustrate, symbolically, the great difference between the Christians' supernatural freedom in Christ, and legalistic bondage to sin and the Law.
Isaac was the supernaturally born 'child of promise', who was born to Abraham and his freeborn wife, Sarah.. in fulfilment of God's covenant-promise with Abraham and His Seed (the Lord Jesus Christ). God promised, that through Isaac would be born the Messiah - the promised “Seed', through Whom the promises God made to Abraham, would finally be fulfilled. The promised Seed would come through Abraham, through Isaac, through Jacob - and through the nation of Israel.
Isaac and not Ishmael was the heir, through whom the Seed would come. Isaac was the son through whom the promised Seed of Abraham would be born, and Paul symbolically compared Isaac, the supernaturally born child of promise.. with Christians, who are also supernaturally born of the Spirit. As children of God we are heirs of the promise.. by the will of God, though faith in Christ.
Ishmael however was the naturally born child of the flesh, who was born to Abraham and Hagar.. the slave-woman. Ishmael was born in fulfilment of human choice, and not the result of God's promise to Abraham. And although he was blessed in many ways.. Ishmael was not the heir of the promise. Paul therefore symbolically linked Ishmael, the child of slavery - with the first covenant - i.e. the Law of Moses, which was made on mount Sinai.
Paul wanted to show that not all Abraham's children are his heirs. Not all are children of the promise. Only those, who by faith are made children of promise, become heirs of God.. while those that are children of the flesh, and enslaved by the Law, are not children of promise. The bondwoman and her son were cast out, which foreshadowed the replacement of the first covenant - where the law of sin and death is replaced with the Law of the Spirit of life in Christ Jesus.
The two women, not only, represented the two covenants, but also the two cities of Jerusalem (the heavenly Jerusalem and the earthly city). Hagar symbolized the First covenant which was cut at Mount Sinai.. and she also represented the earthly Jerusalem, which is in the earthly land promised to Abraham. Sarah however, represents the New covenant of promise, which was cut at Calvary - together with the heavenly Jerusalem.. which reaches its fulfilment in Christ.
This allegory takes the literal, historical context, and uses it to produce an intertextual understanding of the Scriptures. It beautifully demonstrates the freedom Christians have in Christ, because we are free-born children of the God.. and like Isaac, have become children of the promise.
Heavenly Father, thank You for the beautiful, real-life story of Abraham, and the allegory, that Paul used to demonstrate the freedom we have in Christ by faith.. and the bondage we retain, when we seek to live our Christian life according to the works of the flesh - or by following the Law. Thank You that in Christ I am a child of the promise.. having been supernaturally born again by the Spirit. May I jealously guard my freedom in Christ and not be enticed into the legalistic practices that place us back under bondage to the Law - this I ask in Jesus name, AMEN.