The New Perspective on Paul (NPP) is a recent interpretation of Paul’s theology. Basically, the NPP teaches that Judaism in the first century was not marked by works-righteousness per se but rather that Judaism was marked by God’s gracious salvation that resulted in the need for covenantal faithfulness. Covenantal faithfulness included circumcision, festivals, and other Jewish practices. This would mean that Jewish persons of the first century were not trying to work their way into salvation; rather, they did good works (the works of the law) to maintain their covenantal relationship with God.
On this reading, then, Paul called people to faith in Christ because that was a sufficient means to be part of God’s people. To be righteous is to be a member of God’s covenantal family. Righteousness in Paul, according to the NPP, has less to do with personal salvation and more to do with covenantal membership. Paul was calling people to a covenant relationship with God in Jesus Christ through faith and not through circumcision.
With that basic summary said, I should note that the NPP is not a clearly defined theological system. Actually, it would probably be better to call the NPP The New Perspectives on Paul due to the various positions within this camp of Biblical interpretation. So not everyone would agree with my summary above, but I hope that it at least gives some clarity to what the NPP is or might be.
Even though NPP alludes a clear definition, there are certain elements of it that are common. Charles Lee Irons in his 2015 work on The Righteousness of God provides pillars of the new perspective on Paul, which provide some clarity into just what NPP teaches.
“The first pillar is E. P. Sanders’s critique of the older Protestant characterization of Judaism as a legalistic religion and his revised understanding of the pattern of the Jewish religion” (2). God gave a gracious covenant to Israel, and Israelites (later, Jewish persons) obeyed God by doing the works of the law. Doing works of the law marked one as a believer and maintained a covenantal relationship with God.
The second pillar of the New Perspective is “the social function of the law” (3). For NPP persons, Paul did not attack works based salvation (it didn’t exist!). Paul actually rejected the view that a person had to be Jewish or convert to Judaism to be part of God’s people. The works of law are things like circumcision, rituals, and so forth. A person does not need to take part of these works to be part of God’s covenant; they simply need to have faith in Christ.
“The third pillar of the New Perspective is connected to the second, and consists of the lexical claim that Paul’s ΔΙΚ-language is to be interpreted against a Jewish background and hence in covenantal categories” (3). ΔΙΚ is part of a number of Greek words from which we get the English words “just”, “righteous”, “righteousness,” “justify”, and probably others.
Traditionally, to be made just or justified meant that Christ gave us his righteousness. And this gifting saved us because God declared us to be “just” due to Christ’s righteousness in us. For the NPP, to be just or justified means that one is part of God’s covenantal people. God does not declare us just in the traditional sense; he considers us to be members of the covenant.