Tell me, you who desire to be under the law, do you not listen to the law? For it is written that Abraham had two sons, one by a slave woman and one by a free woman. But the son of the slave was born according to the flesh, while the son of the free woman was born through promise. Now this may be interpreted allegorically: these women are two covenants. One is from Mount Sinai, bearing children for slavery; she is Hagar. Now Hagar is Mount Sinai in Arabia; she corresponds to the present Jerusalem, for she is in slavery with her children. But the Jerusalem above is free, and she is our mother.

When we read of the slavery of the present Jerusalem, we know what Paul means because he has told us. He means slavery to the old covenant order, like the Mosaic calendar system and circumcision.

Notice, Paul could have emphasized Abraham’s behavior. He could have said something about the way Abraham did something differently in the case of the two sons. But nothing is mentioned. The TNIV “translators,” thinking this ought to have been Paul’s intent, changed “the son of the slave was born according to the flesh” to “His son by the slave woman was born as the result of human effort.” This is a convenient gloss if one is deadset on insisting that Paul’s primary concern is a false religion of accomplishing salvation by human effort rather than receiving a gracious gift by faith. But it isn’t in the text.

Paul simply follows the narrative flow from Genesis 15 onward:

1. God makes a covenant with Abram involving animal sacrifices
2. Abram takes Hagar and conceives a son who grows up as his heir
3. Later (Genesis 17) God appears and makes another covenant with Abram, changing his name to Abraham and instituting the cutting off of the flesh (circumcision)
4. Abram and Sarah conceive Isaac

From this Paul proclaims that one must be left behind to take the other. You have to choose. You can’t embrace the new creation while demanding that the old creation, the old covenant, remain perpetual.

By the way, here are some other things to read online:

The Nelda Boswell Scroll by Jeff Meyers

A great exposition of Galatians 2.15-21 presented in a fictionalized account of Paul lecturing on his own letter.

The Works of Flesh and the Fruit of Spirit by Jeff Meyers

A story about an event in Galatia that illustrates what Paul’s letter to the Galatians was dealing with.

When the Fullness of Time Had Come: Paul’s Gospel to the Galatians by Derrick Olliff

A great overview of the theology of Galatians. Perhaps the best “one-stop-shop” essay.

The Galatian Heresy: Why We Need to Get It Right by Rich Lusk

A great explanation not only of the theology of Galatians but why it is important specifically for Reformed believers to really take its lessons to heart.

What Saint Paul Should Have Said: Is Galatians a polemic against “legalism”? by Tim Gallant

A clear explanation of how some traditional views of Galatians (while fine in their overall theology) are inadequate on understanding Paul’s specific concerns in this letter.