21Tell me, you who want to be under law, do you not listen to the law?
22For it is written that Abraham had two sons, one by the bondwoman and one by the free woman.
23But the son by the bondwoman was born according to the flesh, and the son by the free woman through the promise.
24This is allegorically speaking, for these women are two covenants: one proceeding from Mount Sinai bearing children who are to be slaves; she is Hagar.
25Now this Hagar is Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children.
26But the Jerusalem above is free; she is our mother.
27For it is written,
“REJOICE, BARREN WOMAN WHO DOES NOT BEAR;
BREAK FORTH AND SHOUT, YOU WHO ARE NOT IN LABOR;
FOR MORE NUMEROUS ARE THE CHILDREN OF THE DESOLATE
THAN OF THE ONE WHO HAS A HUSBAND.”
28And you brethren, like Isaac, are children of promise.
29But as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so it is now also.
30But what does the Scripture say?
“CAST OUT THE BONDWOMAN AND HER SON,
FOR THE SON OF THE BONDWOMAN SHALL NOT BE AN HEIR WITH THE SON OF THE FREE WOMAN.”
31So then, brethren, we are not children of a bondwoman, but of the free woman.
Firstly, this is explicitly described as an allegory, which I had to look up to be certain of its meaning:
“a representation of an abstract or spiritual meaning throughconcrete or material forms; figurative treatment of onesubject under the guise of another.”
So, it should be understood that Paul’s use of this situation is a metaphor, a way to relate and old story with a different meaning so the Galatians can understand what he is saying. the parallel involves the difference between a normal way of behaving (Abraham’s son as a result of relations with Hagar, his wife’s slave) and an occurrence performed by the Holy Spirit (Abraham’s son as a result of God’s intervention with his old and barren wife).
In verse 28, Paul explains that the spiritual descendants of God’s promise to Abraham to be father of a nation. This is exactly the promise that was fulfilled through Christ’s crucifixion. Paul then references the scriptures to continue his comparison to relate how we look at the Law (hagar and her son) and the New Covenant (Sarah and her son). The son of the bondwoman shall not be an heir with the son of the free woman. The Law and Christ’s atonement cannot and will not coexist.
Do we live under the restriction of the Law or live free through the New Covenant?