Then certain individuals came down from Judea and were teaching the brothers, “Unless you are circumcised according to the custom of Moses, you cannot be saved.”…
— Acts 15.1
This is a great summary of the argument for the New Perspective on Paul. The key is the line about Moses. It’s not about works righteousness, but ethnic identity.
And God, who knows the human heart, testified to them by giving them the Holy Spirit, just as he did to us; and in cleansing their hearts by faith he has made no distinction between them and us. Now therefore why are you putting God to the test by placing on the neck of the disciples a yoke that neither our ancestors nor we have been able to bear? On the contrary, we believe that we will be saved through the grace of the Lord Jesus, just as they will.”
Another quick NPP note. Notice here that Peter is not contrasting salvation by yoke versus salvation by grace, but that grace will also save them just as the Jews believed it saved them.