Regardless of your religious beliefs (I'm a very happy aethist) I found Zealot: The Life and Times of Jesus of Nazareth hugely interesting. As a tool to understand the people of the time, the stories that grew and the 'person' behind the dominant religion of the Western World - there is no book that comes close. Don't expect to have fun chats with religious (Christian) friends after reading this though, as much of wh…
Jean Danielou wrote a book about the Dead Sea Scrolls, Qumran, and the Essenes way back in the 80's that explains how it's all related and what it means for Christianity.
I personally had a "not fun" chat with an atheist friend about Zealot because I pointed out how much silly conjecture and assumptions are underlying the book.