We read, Genesis 21:10, that when Sarah saw Ishmael mocking at her son Isaac, she was not able to bear it, but speaketh to her husband Abraham, saying: Cast out this bondwoman and her son; for the son of this bondwoman shall not be heir with my son, even Isaac. The principal design of the apostle seems to be, by that type of the ejection of Ishmael out of Abraham's family, to let them know the mind and will of God:
1. Concerning the exclusion of the law from a partnership with Christ and the gospel, in the justification of sinners before God.
2. Concerning the rejection of the Jews, upon the calling of the Gentiles.
3. Concerning the total destruction of the Jewish church and nation, for their persecution of Christ and the Christian church.