You who want to be under the authority of the law, tell me something. Don't you know what the law says?
It is written that Abraham had two sons. The slave woman gave birth to one of them. The free woman gave birth to the other one.
Abraham's son by the slave woman was born in the usual way. But his son by the free woman was born because of God's promise.
Those things can be taken as examples. The two women stand for two covenants. One covenant comes from Mount Sinai. It gives birth to children who are going to be slaves. It is Hagar.
Hagar stands for Mount Sinai in Arabia. She stands for the present city of Jerusalem. That's because she and her children are slaves.
But the Jerusalem that is above is free. She is our mother.
It is written, "Be glad, woman, you who have no children. Start shouting, you who have no labor pains. The woman who is all alone has more children than the woman who has a husband." (Isaiah 54:1)
Brothers and sisters, you are children because of God's promise just as Isaac was.
At that time, the son born in the usual way tried to hurt the son born by the power of the Holy Spirit. It is the same now.
But what does Scripture say? "Get rid of the slave woman. Get rid of her son. The slave woman's son will never have a share of the family's property with the free woman's son."(Genesis 21:10)
Brothers and sisters, we are not the slave woman's children. We are the free woman's children.