The New Perspective came out of a shift in understanding Paul's writings in the context of Second Temple Judaism.
In particular, some scholars felt that many of the Lutheran and Reformed views interpret Paul too much in the context of 16th-century Roman Catholicism rather than 1st-century Judaism. In other words, they project on to Paul's opponents too much of their own opponents.
So the New Perspective is firstly an attempt to better understand what 1st-century Jews thought and hence what Paul's issue with them might be.