Always read the Preface to any book. In this Preface, world renowned New Testament scholar, Ben Witherington III says this:
There are several good reasons such a study is needed not only by Bible students and budding scholars but also by pastors and laypeople at this juncture: (1) A profound historical amnesia is affecting even churches that are bibliocentric. They don't know the history of the Bible or the history of the struggle to affirm its final authority in Christian life. What exactly does the phrase "only Scripture" really mean, and what are its implications? . . . 
This is the main question answered in this book. And answering that question, resolves so many others.