Now this may be interpreted allegorically: these women are two covenants. One is from Mount Sinai, bearing children for slavery; she is Hagar. Now Hagar is Mount Sinai in Arabia; she corresponds to the present Jerusalem, for she is in slavery with her children…But what does the Scripture say? “Cast out the slave woman and her son, for the son of the slave woman shall not inherit with the son of the free woman.” So, brothers, we are not children of the slave but of the free woman. (Galatians 4:21-25, 30-31)

Paul is saying here, via allegory, that Jerusalem as it was in his day was cast out. He said that Jerusalem was Hagar and then cites scripture that says Hagar and Ishmael were rejected.

And if you consider the context of the quote from Genesis 21 what God told Abraham to do was follow the wishes of his wife Sarah “for through Isaac shall your offspring be named.” This promise of offspring, according to Galatians 3, is the promise of Jesus and the promise was given in the form of a covenant. The blessings of the covenant would come through Isaac, not Ishmael therefore Ishmael was to be cut off and sent away. So what Paul is saying in chapter 4 through this allegory is that Jerusalem was cut off from the blessings of Abraham’s covenant. That doesn’t mean that God is going to completely ignore Israel any more than he was abandoning Ishmael. God promised Abraham “As for Ishmael, I have heard you; behold, I have blessed him and will make him fruitful and multiply him greatly. He shall father twelve princes, and I will make him into a great nation. But I will establish my covenant with Isaac, whom Sarah shall bear to you at this time next year.” (Genesis 17:20-21)

The covenant doesn’t belong to national Israel because they rejected the promised Offspring and choose instead to remain under the law. God may still bless them, indeed history seems to show that he is still watching over them, but the covenant is with Sarah and her children. This is why at the end of the letter to the Galatians when Paul picks up the pen himself, he says “And as for all who walk by this rule, peace and mercy be upon them, and upon the Israel of God.” (Galatians 6:16) The rule is a rejection of circumcision and blessing is upon those who agree with that and the Israel of God, that is, the offspring of the free woman, the church.

This is really just a fragment of a larger discussion on the covenant and the place of Israel in it. This little post doesn’t say all that is to be said on that subject. Consult a theologian before using this post.