Thematic Bible: Isaac born to

For Sarah became pregnant and bore Abraham a son in his old age, at the set time God had told him. Abraham named his son whom Sarah bore to him Isaac [laughter].

For it is written that Abraham had two sons, one by the bondmaid and one by the free woman. But whereas the child of the slave woman was born according to the flesh and had an ordinary birth, the son of the free woman was born in fulfillment of the promise. Now all this is an allegory; these [two women] represent two covenants. One covenant originated from Mount Sinai [where the Law was given] and bears [children destined] for slavery; this is Hagar. read more.
Now Hagar is (stands for) Mount Sinai in Arabia and she corresponds to and belongs in the same category with the present Jerusalem, for she is in bondage together with her children. But the Jerusalem above ( the Messianic kingdom of Christ) is free, and she is our mother. For it is written in the Scriptures, Rejoice, O barren woman, who has not given birth to children; break forth into a joyful shout, you who are not feeling birth pangs, for the desolate woman has many more children than she who has a husband. But we, brethren, are children [ not by physical descent, as was Ishmael, but] like Isaac, born in virtue of promise. Yet [just] as at that time the child [of ordinary birth] born according to the flesh despised and persecuted him [who was born remarkably] according to [the promise and the working of] the [Holy] Spirit, so it is now also. But what does the Scripture say? Cast out and send away the slave woman and her son, for never shall the son of the slave woman be heir and share the inheritance with the son of the free woman.