Thematic Bible: Isaac born to

For Sarah conceived and bore Abraham a son in his old age at the set time of which God had spoken to him. And Abraham called the name of his son that was born unto him, whom Sarah bore to him, Isaac.

For it is written that Abraham had two sons, the one by a bondmaid, the other by a freewoman. But he who was of the bondwoman was born according to the flesh, but he of the freewoman was born through the promise. Which things are an allegory; for these women are the two covenants: the one from the Mount Sinai, which begat unto slavery, which is Hagar. read more.
For this Hagar or Sinai is a mount in Arabia, which corresponds to the one that is now Jerusalem, which together with her children is in slavery. But the Jerusalem of above is free, which is the mother of us all. For it is written, Rejoice, thou barren that bearest not; break forth into praise and cry, thou that travailest not: for the desolate has many more children than she who has a husband. So that we, brethren, as Isaac was, are the children of promise. But as then he that was born according to the flesh persecuted him that was born according to the Spirit, even so it is now. Nevertheless what does the scripture say? Cast out the bondwoman and her son, for the son of the bondwoman shall not be heir with the son of the freewoman.