We are saved, not by works but by the grace of God.

We are saved, not by works but by the grace of God.
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Galatians 4:21-31
New Living Translation (NLT)

Abraham’s Two Children
21 Tell me, you who want to live under the law, do you know what the law actually says? 22 The Scriptures say that Abraham had two sons, one from his slave wife and one from his freeborn wife.[a] 23 The son of the slave wife was born in a human attempt to bring about the fulfillment of God’s promise. But the son of the freeborn wife was born as God’s own fulfillment of his promise.

24 These two women serve as an illustration of God’s two covenants. The first woman, Hagar, represents Mount Sinai where people received the law that enslaved them. 25 And now Jerusalem is just like Mount Sinai in Arabia,[b] because she and her children live in slavery to the law. 26 But the other woman, Sarah, represents the heavenly Jerusalem. She is the free woman, and she is our mother. 27 As Isaiah said,

“Rejoice, O childless woman,
you who have never given birth!
Break into a joyful shout,
you who have never been in labor!
For the desolate woman now has more children
than the woman who lives with her husband!”[c]

28 And you, dear brothers and sisters, are children of the promise, just like Isaac. 29 But you are now being persecuted by those who want you to keep the law, just as Ishmael, the child born by human effort, persecuted Isaac, the child born by the power of the Spirit.

30 But what do the Scriptures say about that? “Get rid of the slave and her son, for the son of the slave woman will not share the inheritance with the free woman’s son.”[d] 31 So, dear brothers and sisters, we are not children of the slave woman; we are children of the free woman.

Excerpt from day 3
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Delving into the symbolism deeper, Paul talked about the mothers as well. Hagar was a
slave and she gave birth to a slave (Ishmael). They represent the covenant from Mount
Sinai, and in the New Testament time, correspond to the earthly Jerusalem, i.e. the Jews
then who were trying to gain salvation by obeying the Law.

On the other hand, Sarah was a free woman and she gave birth to a free man (Isaac).
They represent the New Covenant, and correspond to the heavenly Jerusalem, i.e. the
New Testament believers in Christ – people who are saved, not by works but by the
grace of God.

Paul goes on to quote Isaiah 54:1 about the barren woman having more children than
the one who had a husband. The background to this verse would be the Abraham-­‐
Sarah-­‐Hagar account in Genesis. Recall that Sarah was barren. This was why Hagar
came into the picture, and she was pregnant soon afterwards. Perhaps there was
gloating on the part of Hagar, mocking at the barrenness of her mistress Sarah while
she was bearing Ishmael. Yet her happiness didn’t last long! Before long, she would be
cast out of the house together with Ishmael, while Sarah would bear a son, the son of
promise – Isaac.

The immediate context of Isaiah 54:1 was about the return of the Jews from exile, and
how God here promised that though they looked like the barren woman, yet He shall so
blessed them that they shall have many children. One cannot help but relate this to
God’s blessings to Abraham in Genesis that his descendants be as numerous as the
sand of the sea and the stars of the sky.

When and how would this promise to Abraham, and the promise of Isaiah 54:1, come
to pass? It would ultimately be fulfilled in the Christian Church! Those who believed in
Christ for justification are the true sons of Abraham, free persons like Isaac, and they
are the “many more children” of the barren woman!

Overall, Paul is saying to the Galatian Christians: It is not enough to claim Abraham as
your father. You must also know who is your mother. If she is Hagar, then you are like
Ishmael, but if she is Sarah, then you are like Isaac.

Reference:
http://shalomrb.org/RTBT/Galatians.pdf