If you have read the other reviews, you already know that Bishop Spong quckly sets aside the literal "Christmas Story" and the "Virgin Birth" in this book. Much more intersting to me, however, was his careful tracing of the crafting of what we know today as the "Christmas Story" in the order the various references were written, starting with Paul (I didn't realize his account was written earlier than the gospels).
The core of this book is Bishop Spong's combination of the few clues in the Bible with the intellectual and political currents of the day in the early church, and how they effected the moulding of the traditions we know today as the "Christmas Story" and the "Virgin Birth".
When he has finished his interesting analysis, he then adds a final chapter to discuss how he feels the developing concept of the "purity of Mary" has influenced the state of women in the centuries since, to the present day. While this is somewhat disconnected from the rest of the book, it builds on the lessons of the previous chapters, and opens up the possibility of dialog on the subject.
There is no question that this book has and will offend many Christians, but for those who are intellectually curious and like to think "out of the box", this book is a treat.