In this text Hagar the bond woman is compared to Sarah, the free woman and their children Isaac and Ishmael are also constrasted.
Ishmael was born after the order and process of nature, and as such, he was born into slavery, being born of a slave girl; born because of the work, effort, human reason and will of Sarah. He was born because of fleshly impulses, urges, and attraction of Abraham. Isaac however, was born as a freeman, born of a free woman, Sarah, born by the promise of God alone.
The two mothers and their sons serve as an allegory comparing the Old Covenant with the New, the Law with the Gospel, the earthly Jerusalem with the heavenly one. Ishmael represents the persecuting world while Isaac the persecuted Christian. Ishmael is in the end cast out while Isaac is an heir to the inheritance. Which are you?
