I've been doing a lot of thinking in Galatians 2. Ever since the ground breaking work of those belonging to the “New Perspectives on Paul” New Testament scholarship has become dominated by a line of thinking that justification is not the result of faith in Christ, but by the faith of Christ.
Since Luther Protestants have understood justification to be the means by which an individual appropriates salvation. Paul, it was argued, was talking about being justified by faith, not by works – which was the route taken by Judaism. However, in the revolution that's been taking place in Pauline scholarship over the last thirty years justification has come to be seen in a new light. This is largely due to the fact that first-century Judaism(s) is (are) starting to be respected for what it truly was instead of being seen through the lens of Luther's critique of the medieval Catholic church. In Judaism at the time of Paul justification was never about how one appropriates salvation. Rather, it was about badges of membership. Instead of being about how one enters the people of God it is about how one can tell who already is a member of God's people. This resolves the problem that often comes with the old approach to justification: that of faith just being another work one does to earn salvation. No, according to Paul, faith is a badge of membership not another surrogate work. Therefore Paul's argument with the trouble-makers in Galatia was about what defines God's people. Paul emphatically argues that works of the Law (understood as circumcision, food-laws, and observance of Sabbath) are no longer the badges of membership. Those who are in Christ are marked by the faith of Christ.
Of course this has already been said before by the likes of Wright and Hays and Dunn.
Now here's where it could get interesting…
I am IN Christ because of the faith OF Christ. In fact, I am so much in Christ that I have been crucified with him and it is now he who lives through me (Galatians 2). That means that the faith I possess is also the faith OF Christ. However, if I was justified by Christ's faith, and I now embody Christ's faith are not those around me justified by my faith?