The late 20th century saw the rise in biblical scholarship of what was called the "new perspective" on Paul, the third quest for the historical Jesus, and re-investigations of the "parting of the ways" between Christianity and Judaism. What was that all about? Basically, it was the fact that it took until the late 1970s for Christian scholars to recognize the Lutheran glasses that they had been wearing to interpret the New Testament and Judaism for centuries.
The new perspective was not just a new perspective on Judaism. It also involved some modification to the understanding of early Christianity. There has been much debate over the new perspective, especially in Reformed and Lutheran circles. And while there was much push-back and "new perspective" remains a dirty phrase in some circles, I don't know that you will find any scholars anywhere who haven't made some adjustments to their understandings after the debates of the last 40 years.
On the side of Judaism, new perspective was being honest about the fact that there was far more grace in the Jewish literature of Paul's day than the paper cut-out that had been in use in the 1800s and early 1900s, especially in German scholarship. Joachim Jeremias is so off on some things that E. P. Sanders was tempted to think he was intentionally skewing his account of Judaism at some points.
The stereotype of legalism, as if all Jews were like the Pharisees of Matthew 23, just doesn't fit what the Jewish writings of the time say (such as the hymns of the Teacher of Righteousness in the Dead Sea Scrolls). Reformed folk like D. A. Carson launched a push-back project called, Justification and Variegated Nomism to try to undermine the new perspective's understanding of Jewish literature. But the entire project more less confirms that Judaism wasn't this "works-righteousness" type hypocrisy that was par for the course before 1977. Even those pushing back have already modified their understanding of Judaism.
On Paul's side, those of us in the Wesleyan tradition can be happy to find that the new perspective actually says what we have said all along. The Reformed tradition has always accused us of works-righteousness in our interpretation of Paul. So it's no surprise that they would reject the new perspective when it more or less said what we have said all along--Paul expected a Christian to demonstrate fruit of righteousness in Christian living, and those who do not are in danger of not making it into the kingdom.
So the new perspective suggested that Paul and the rest of the New Testament believed that righteousness was a central part of Christian living. Similarly, it suggested that grace was an essential feature of Second Temple Judaism. It took the Lutheran and Augustinian glasses off of our reading of Judaism and Paul, which prompted a wholesale re-evaluation. That eval spread to Jesus (thus the "third" quest) and eventually to a re-examination of when Christianity really became a distinct religion from Judaism.
The result has been a much fairer perspective on both, more or less calling into question any resource on Paul or Judaism before about 1980.