Through the years I've read a good few books on progressive theology—on both sides of the issues. (And there are many!) An interesting book worth reading is Wildfire: How Progressive Theology is Impacting the Church. The author is Daren Overstreet (Tampa, FL). Wildfire is well researched.
From the back cover: "Do you get the feeling something significant is shifting under your feet—not only in society, but even in the church? It’s unsettling when you don’t quite know what it is or why it’s happening. This book identifies a major cause of that shift and why it is occurring, making it a must-read for all who care about the future of God’s church. With deep humility and care, Daren Overstreet directs our attention to the cracks are forming in our foundation, and to the impending wildfire looming on the horizon—along with a biblical response to both" (Jeff Chacon).
In the words of one reviewer, "A careful and relevant analysis of the issues facing the church today. Wildfire clarifies the concepts and definitions encompassed in Progressive Theology, examines their impact, provides extensive insight from a number of sources, and uses scripture as the ultimate criterion for assessing the merits of this movement... Daren Overstreet has equipped the church for thoughtful and fruitful conversation..."