Paul’s comments in Galatians 3:11-12 are often read as contrasting the Mosaic Law with the Christian gospel, or Judaism and Christianity. I’ve noted recently that I think this is a misreading, both of Paul in general and Galatians in particular.
In my opinion, Paul is arguing with reference to the specific choice before his Galatian converts. That is, he isn’t making timeless theological claims about the Mosaic Law but situation-specific assertions about gentiles converting to Judaism in order to be fully accepted before God.
I’ll have lots more to say about this over the next few months as I work through Galatians, but for now, here’s my expanded (albeit somewhat clunky) translation of Gal. 3:11-12:
Now because one’s ethnic identity—in this case being Jewish—is irrelevant for justification before God, it is obvious that God’s approved response to the gospel of Christ is faithfulness. And to respond to the gospel by being circumcised and converting to Judaism is not how you ought to be embodying faithfulness, which brings God’s approval; rather, the one who responds to the revelation of Jesus Christ with faithfulness will enjoy life from God.