What then do the Writings say? Send away the servant-woman and her son; for the son of the servant-woman will not have a part in the heritage with the son of the free woman.

Because it is in the Writings, that Abraham had two sons, one by the servant-woman, and one by the free woman.

Now the son by the servant-woman has his birth after the flesh; but the son by the free woman has his birth through the undertaking of God.

So, brothers, we are not children of the servant-woman, but of the free woman.