In reading up on Isaac and Ishmael, I came across this from James Jordan:
The allegory is related to Revelation 12:14-17. The Woman who gave birth to the Son is taken into the wilderness to be protected from the Dragon. The Dragon pours out the defiling water of false (Judaizing) doctrine to try and corrupt her, but God protects her as the Apostles fight the Judaizers with the true cleansing water of truth. Then the Dragon moves out and attacks the other part of the Woman’s Seed, the Gentile part of the Church, by raising up the Roman Beast. Thus, the Woman in the wilderness and the children with her are the Jewish believers, driven out in Acts 8 after Satan began putting them to death in Acts 7.
The Woman in Revelation 12 is the entire First Creation church, from Eve to Mary, including Hagar. It is Hagar’s experience that is alluded to in 12:14-16. Paul has said that the Jews are Hagar and Ishmael. They are the original household of Abraham, after which came Sarah and Isaac. The converted Jews, like Hagar and Ishmael, flee into the wilderness. The original Hagar found that the “old water” of Abraham ran out, and could not find any new water until God provided it. This is an allegory of the gospel: The water of the Old Creation kingdom is running out, and people must seek the new water of the New Creation. In a similar way, the Hagar-Woman of Revelation 12 has left the old water. Satan offers counterfeit new water, flowing from his Wormwood occupation of Herod’s Temple (Revelation 8:10-11). The false unconverted Jews drink up this evil water, and by implication, God provides new water, from the New Jerusalem, for the Hagar-Woman and her Ishmael-child in the wilderness.