It is written that Abraham had two sons, one by the slave and the other by the free woman. The child of the slave was born in the ordinary course of nature, but the child of the free woman was born in accordance with God’s promise. This can be regarded as an allegory. Here are the two agreements represented by the two women: the one from Mount Sinai bearing children into slavery, typified by Hagar (Mount Sinai being in Arabia, the land of the descendants of Ishmael, Hagar’s son), and corresponding to present-day Jerusalem—for the Jews are still, spiritually speaking, “slaves”. But the free woman typifies the heavenly Jerusalem, which is the mother of us all, and is spiritually “free”. It is written: ‘Rejoice, O barren, you who do not bear! Break forth and shout, you who do not travail! For the desolate has many more children than she who has a husband.’
Tell me now, you who have become so enamored with the law: Have you paid close attention to that law? Abraham, remember, had two sons: one by the slave woman and one by the free woman. The son of the slave woman was born by human connivance; the son of the free woman was born by God’s promise. This illustrates the very thing we are dealing with now. The two births represent two ways of being in relationship with God. One is from Mount Sinai in Arabia. It corresponds with what is now going on in Jerusalem—a slave life, producing slaves as offspring. This is the way of Hagar. In contrast to that, there is an invisible Jerusalem, a free Jerusalem, and she is our mother—this is the way of Sarah. Remember what Isaiah wrote: Rejoice, barren woman who bears no children, shout and cry out, woman who has no birth pangs, Because the children of the barren woman now surpass the children of the chosen woman. Isn’t it clear, friends, that you, like Isaac, are children of promise? In the days of Hagar and Sarah, the child who came from faithless connivance (Ishmael) harassed the child who came—empowered by the Spirit—from the faithful promise (Isaac). Isn’t it clear that the harassment you are now experiencing from the Jerusalem heretics follows that old pattern? There is a Scripture that tells us what to do: “Expel the slave mother with her son, for the slave son will not inherit with the free son.” Isn’t that conclusive? We are not children of the slave woman, but of the free woman.
The Holy Writings say that Abraham had two sons. One was born from a woman servant (Hagar) who was owned by someone. She had to do what she was told. The other son was born from a woman (Sarah) who was free to work and live as she desired.