For it is written that Abraham had two sons, one by the slave woman1 and the other by the free woman.223
His son by the slave woman was born in the ordinary way;3 but his son by the free woman was born as the result of a promise.424
These things may be taken figuratively, for the women represent two covenants. One covenant is from Mount Sinai and bears children who are to be slaves: This is Hagar.
Now Hagar stands for Mount Sinai in Arabia and corresponds to the present city of Jerusalem, because she is in slavery with her children.
But the Jerusalem that is above5 is free, and she is our mother.
For it is written: "Be glad, O barren woman, who bears no children; break forth and cry aloud, you who have no labor pains; because more are the children of the desolate woman than of her who has a husband."a628
Now you, brothers, like Isaac, are children of promise.729
At that time the son born in the ordinary way8 persecuted the son born by the power of the Spirit.9 It is the same now.
But what does the Scripture say? "Get rid of the slave woman and her son, for the slave woman's son will never share in the inheritance with the free woman's son."b10