I guess today is Machen day. I'm working on the part of my dissertation that deals with Gal 1:13-14, Paul's conversion and pre-conversion past, so I've been dipping into Machen's The Origin of St. Paul's Religion, a series of lectures he delivered in 1925 (as a 300-pg book I wonder how long he lectured for!). He has a gem toward the end. He is arguing against Wrede and an idea that has connections with the current New Perspective (Dunn and Watson e.g.)--the idea that justification by faith only truly came home to Paul, became meaningful and important, as the apostle dealt with gentile inclusion in the people of God. Machen writes:
Nothing could be more utterly unhistorical than the representation of Paul as a practical missionary, developing the doctrine of justification by faith in order to get rid of a doctrine of the Law which would be a hindrance in the way of his Gentile mission. Such a representation reverses the real state of the case. The real reason why Paul was devoted to the doctrine of justification by faith was not that it made possible the Gentile mission, but rather that it was true. Paul was not devoted to the doctrine of justification by faith because of the Gentile mission; he was devoted to the Gentile mission because of the doctrine of justification by faith. (Origin of Paul's Religion, 1978 Eerdmans, repr, 278-79)
That is exactly right.