Like so many modern books on business and leadership - the book can be quickly summarized in a few points. The book itself narrates numerous stories to illustrate the truths of these points.
In truth, the core of the book is summarized - for all intent and purposes - in these links provided at the Table Group's website:
Their Organizational Health Model
I've worked in the Church and in Church based Universities for my professional career. By virtue of a commitment to the mission of Christ - and by virtue of the hybrid nature of leadership that is diffuse among various campus realities (Schools within Universities, Department Leadership vis-a-vis Deans vis-a-vis Administrators) - the organizations I've worked in do not fit the same type of organizations that Lencioni describes.
Nevertheless, I still wish I could work in an organization - or within organizations - that had the clarity & vision & openness & vulnerability & accountability & trust that Lencioni articulates. I would love to sign up for leadership in an organization to help it develop in these ways!
Even though you can "read" the book's data in the links I've provided, I still recommend the book for it's stories that "flesh-out" the concepts.