What did Paul mean in his rebuke of Peter in Galatians 2:11-14? (Q&A)

Q:  I’m almost finished reading your Jewish Roots of Christianity book. I’ve appreciated learning so much history that I never knew, but it makes me sad to think that people who have called themselves by the name of Christ have acted so horrendously… It helps me to understand a little better the anti-Semitism that we saw (and were SHOCKED by) in Ukraine.

I’m meditating on the thought that you bring forth in the book that Messianic Jews still need to follow the law… What do you do then with Paul’s remarks in Galatians 2:11-14, where Paul calls Peter on the carpet for reverting back to following the laws when the circumcision party shows up in Antioch? Paul certainly talks here, and in other places, like he is not following the dietary laws at least…