The chapter on Galatians in A Biblical-Theological Introduction to the New Testament: The Gospel Realized is helpful for understanding the structure of the book. In our discussion of the New Perspective on Paul, the main figure in mind is N. T. Wright. He has several books on Paul at various levels of intensity. What Saint Paul Really Said is accessible, but represents an earlier version of his ideas. But, it is helpful for the average person to grasp his different reading of books like Galatians. For a different perspective on the New Perspective, interested readers should pick up Justification Reconsidered by Stephen Westerholm. As always, check out the Bible Project video on Galatians: https://youtu.be/vmx4UjRFp0M