"Jesus of Nazareth," Pope Benedict's first book since being elected pope, has been the bestselling book in Italy ever since it hit the bookstores more than two weeks ago, and worldwide sales are expected to explode as it hits bookshelves in other countries.
Fifty thousand copies were sold on the first day it hit the shelves, April 16, and more than 500,000 copies of the book have been printed and distributed to bookstores throughout Italy.
More than 480,000 copies have been printed in Germany, where the book is selling on average between 20,000 to 30,000 copies a day, and more than 100,000 copies have been printed in Poland.
These three language editions were the first to be published, and up to 22 other language editions are expected to appear in bookstores around the world in the coming months -- including the Korean, Slovenian, Greek and Maltese language editions.
The U.S. edition is being published by Doubleday and will be on sale starting May 15.
"Jesus of Nazareth," the first part of a two-volume work, is a highly complex theological treatise on Christ as both God and man. In over 450 pages, using hundreds of Biblical references, citations and quotes, the pope uses careful analysis of passages in the Gospels to make his point and defend the reliability of their accounts of Jesus.
Pope Benedict, a prolific writer on theological matters and a former university theology teacher and former head of the Vatican office for church doctrine for almost 25 years, is considered one of the leading theologians in the Catholic Church.
He has stressed, however, that the book is his personal vision, not an infallible part of official Church teaching, and that anyone can contradict him. Both the names Joseph Ratzinger and Benedict XVI appear on the book's cover.
The pope, 80, started work on this book almost two years ago when he was still a cardinal, before he was elected pope. He finished the first 10 chapters last September.
He decided to go ahead and publish the first part of his work and is reportedly already at work writing the second volume, which will deal with the birth of Christ, his crucifixion and resurrection.
Many who have read the book believe that this book is a key to understanding Pope Benedict's theological thinking and the roots of his Christian faith.
"What always surprises me, in a good sense, is the capacity of this pope to blend together thoughts about science, faith, reason and spirituality," a Vatican spokesman, Father Federico Lombardi, said to ABC News.
Marco Politi, a Vatican reporter for the Italian newspaper la Repubblica, told ABC News that the pope's book is "certainly his answer to books that question the divine nature of Christ."
Politi, a longtime Vatican watcher, believes Pope Benedict's book will be as successful as his first encyclical, "God is Love", has proven to be. Politi said the pope hopes to confirm and reassure his flock with this book.
"Certainly, there is a part of Christianity, of the Catholic world who wants to have a strong identity and this pope reassures these people."
The Austrian Cardinal Christoph Schonborn, who presented the book at the Vatican on May 13 and has known the Pope for over 30 years, told ABC News that although the book did not shed any new surprising light on the pope's character, he was surprised by it.