Galatians 4 21-31 Hagar and Sarah

It's Storytime
If the Galatians love the Torah so much, maybe they'd like to hear a story from the Torah. Yeah, Paul thought they would.

Remember Abraham and his two sons, Ishmael and Isaac?
Hagar was the mother of Ishmael. She was a slave woman whose son came into the world in the usual way (i.e., sex). Boring, right? No she represents those who received the covenant of Moses give on the Mountain
But Sarah, the mother of Isaac, was infertile, and God himself allowed her conceive a child. Isaac, therefore, came into the world through God's promise. The Covenant of Abraham.
Paul thinks that the two women represent two different paths.
Hagar was a slave and bore children who would become slaves (to the law).
But Sarah was free and she gave birth because of God's goodness and love.
As a gentile believer we are brought into the the Covenant with G_d due to circumcision or obedience to the law but due to an earlier covenant which says thought Him all the nations of the world would be brought in.