What specially is new and different in the "New Perspective on Paul" movement? How can the differences to the "old" perspective be summarized?
Note: Please don't make this question about defending one view over the other, only concisely describing any significant differences between them.
The NPP includes more than just a new set of interpretations for Paul's works, it also re-examines several other historical issues and purports to throw a different light on them. In reading through material from both sides, I find that much breath seems to be wasted on detailed analysis of issues that aren't actually new or different in any way, but that a few key issues (particularly the definition of Justification) are substantially different. While some NPP adherents claim that their new view of Justification is compatible with the old, most who hold the old view find the new to be incompatible.
Full disclosure: I believe that, while the NPP has some valuable perspectives to offer Christianity, some of its premises are invalid and some of its conclusions are heretical. Still, I will try to answer here carefully. If my treatment of the facts of the case are not fair, feel free to comment.
The basis for the "new" understanding of Paul's life and teachings is really rooted in a different understanding of the religious culture of his day.
Historically, most of Protestantism has understood 1st century Judaism to be a works-based religious system under which people crossed their t's and dotted their i's in accordance with a vast set of laws and regulations in order to earn or deserve God's favor. NPP submits that Judaism in Paul's time was actually more about grace than Reformation era Protestants give it credit for: that it taught grace as the basis of salvation and works as a basis of judgement, not works as the basis of salvation.
If 1st Century Judaism wasn't a religion of works, then Paul's discourses on it must not have been raising that as an objection. If he was actually in agreement with Judaism on the issue of works vs. grace, then the contrasts we find in his teachings between works and grace must not have been a matter of right vs. wrong religion -- as most Reformed teachings claim -- but one of two parts of the same right religious understanding being contrasted. Hence, the NPP would have works and faith working together in the effecting of salvation.
With works and faith working together rather than one being the result of the other, Wright and others from the NPP movement must also recast the doctrine of imputed righteousness. Rather than Christ's work being the sole item to the credit of our accounts, our own works will be part of our judgement. Wright does not believe that God's righteousness can actually be transferred to anyone, only that he can declare (law court terminology) people to be in good standing; their own righteousness will still be based on their own works.
I'm not a theologian but my understanding is that what's "new" is the move away from the traditional reformed view of justification by works vs. by faith. Wright does not deny this but believes that the traditional view misunderstands and oversimplifies what Paul meant, taking "works" to mean any human effort or action. Wright, I think, sees these "works" in terms of the things that established covenant membership (primarily circumcision). So the "new" view includes that Paul's works-faith dichotomy means something more like "belonging to God's people is not only for the Jews but for everyone." I could be all wrong though! See the series on JesusCreed about the New Perspective.
If the "new" perspective belief is accurate, then the actual answer is "nothing". The New Perspective on Paul attempts to get back to the original intent of Paul's letters by explaining the issues he was addressing when he wrote them. The movement asserts that our current teachings and understanding of his letters are based on a misunderstanding of the original intent.
The perspective is "new" only in the sense that a used car can be referred to as "my new car" to the person who just bought it. It's new to the current audience, but really, it's not new at all.
The difficulty in answering how it compares to the "old" perspective (and the reason I think the question stayed unanswered for so long) is that there's a lack of agreement on what the "old" perspective is. Consider the following stances that varying disciplines take on salvation, for example:
So to compare the "new" perspective to the "old" perspective, you need to ask which "old" perspective?
At best, the New Perspective, from what I've been reading since you posted the question is that it merely lends support for an existing perspective - tat you must be within the fold, and your good works are a sign that you are in the fold. It's a combination of several of the above beliefs into one , possibly new, doctrinal stance.
This is perhaps over-simplified, but in essence, the "new perspective" results in the following theological stance on salvation:
