Summary: Paul uses the story of Ishmael and Isaac and their mothers to demonstrate that the Galatian believers were in danger of abandoning the Gospel of grace in Jesus, with fascinating contrasts historically and allegorically, ever relevant for today.
THE SPIRITUAL SAGA OF ISHMAEL AND ISAAC
The most casual reader of the Bible will notice that the Scriptures consist of 2 sections - the Old and New Testaments. But have you ever thought how are they related to each other? Someone made the interesting comment about the 2 Testaments that are God’s revelation of himself: "The New is in the Old concealed; the Old is in the New revealed."
There are many passages in the Old Testament which seem on the surface to serve only as historical accounts of God’s dealings with early members of the human race and their relationships with each other. The stories are interesting in themselves and throw light on human nature. But then they are picked up in the New Testament and are shown to have a deeper and a spiritual meaning in the purposes of God. The personalities and their actions are seen as symbols of spiritual truth, as living illustrations to illuminate some aspect of the Christian faith.
Christianity is a faith religion - faith in Jesus Christ, but its roots can be traced back to Abraham to whom God gave such great promises. We are going to look at Abraham’s two sons - Ishmael and Isaac - and see how the principles of our faith are illustrated. We take as our authority for doing so none other than the Apostle Paul. The readings from Genesis 16:1-10 (quickview) ,15; 17:1-8 and Galatians 4:21-31 (quickview)  will be our guide as we explore:
THE CONTRAST BETWEEN THE OLD TESTAMENT LEGAL CODE AND THE NEW TESTAMENT FAITH
When Paul was writing to the Christians in Galatia, a region in what is now modern Turkey. He was most concerned that these converts to Christianity were in danger of making shipwreck of their journey in the Christian faith and the Holy Spirit turned his thoughts back to the founding father of the Jewish religion to make these new Christians see that they were way off course. His thinking was that if the unchanging God had revealed the way of faith to Abraham, that principle held true for all time.
What a good thing that the Apostle was steeped in the Old Testament. Yes, it had its fulfilment in the New Testament but its principles held good and could be used profitably in shedding light on current problems. I wonder if we value the Old Testament in the same way? It is Scripture; it can be our guide and inspiration if we read it, as someone put it, "with New Testament spectacles"!
Well, what was the problem that Paul found in the experience of the Galatian Christians? They had become unfaithful to the gospel of Christ as a result of the corrupting influence of false teachers. Paul was utterly amazed that they had left the purity of their faith in Christ. It was a kind of spiritual treason; an act of great folly. Paul could hardly believe that they would do such a thing. "O foolish Galatians!" says Paul (3:1). J B Phillips puts it in more colourful language, "O you dear idiots of Galatia … surely you can’t be so idiotic?" What would be your reaction if your pastor used such terms to you? What had they gone and done? They had fallen for the false teaching of some travelling Jewish teachers who said that Christianity wasn’t complete without the ritual observance of the Jewish law. Paul said that this was a contradiction of the Gospel.