What does the Scripture say about this matter? [It says, Gen. 21:10-12], "Get rid of the slave woman [Hagar], with her son [Ishmael]; for the son of the slave woman [Ishmael] will not inherit [what God promised to Abraham and his descendants], along with the son of the free woman [i.e., Isaac]."

For it is written in the law about Abraham's two sons [Gen. 16]; one [was] by his slave woman [Hagar] and the other by the free woman, [his wife, Sarah].

Now the son [Ishmael], born to the slave woman, was born simply of their natural relationship; but the son [Isaac], born to the free woman, was born in fulfillment of a [divine] promise.

For it is written [Isa. 40:1], "[Woman] you should be happy that you have not had children. Cry over your inability to experience the pain of childbirth. For the deserted woman has had more children than the one with a husband."

Therefore, brothers, we [Christians] are not the [spiritual] children of the slave woman [Hagar] but of the free woman [Sarah].