On Christian Liberty by Martin Luther (book)

http://www.amazon.com/Christian-Liberty-Facets-Martin-Luther-ebook/dp/B00APJRSN8/

This book is simply THE BOOK to read to understand Protestantism, both the good and the bad.  Obviously you have to read the Old Testament and New Testament before reading this.

I wrote a long post of my impressions after reading this book here:

http://www.coalpha.org/Concerning-Christian-Liberty-by-Martin-Luther-book-tp7088478.html