5 books about Paul just won't do. It has to be seven.
Previously, I recommended Paul: A Very Short Introduction by E.P. Sanders. So that moves yesterday's post to six.
And then there is perhaps my all time favorite: The Gospel According to Paul by A. M. Hunter. It is now out of print, but still a model of concise writing that organizes Paul's thought into easy to understand categories. You can still find copies at used book stores and among the used offerings at Amazon. This really is a great little book and rounds out our list of resource books on Paul to a more perfect seven.