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].

Which things contain an allegory: for these women are two covenants; one from mount Sinai, bearing children unto bondage, which is Hagar.

Now this Hagar is mount Sinai in Arabia and answereth to the Jerusalem that now is: for she is in bondage with her children.

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]."

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