“Benedict XVI did theology on his knees,” the pope wrote in the book’s introduction. “His explanation of the faith was carried out with the devotion of a man who has surrendered all of himself to God.”

Archbishop Georg Gaenswein’s “Nothing but the Truth: My Life Beside Pope Benedict XVI” is being published this month by the Piemme imprint of Italian publishing giant Mondadori.

Zen was elevated to cardinal by Benedict in 2006, which he said signaled the pope’s focus on China.

Though he is criticized for the sexual abuse crisis in the church during his papacy, Benedict XVI did more than anyone before him to turn the Vatican around on clergy sexual abuse.

The only thing certain is that the most important ritual following the death of a pope—a conclave to elect a new one—does not apply.

The pope’s letter, titled "Totum Amoris Est" ("Everything Pertains to Love"), said that the saint has much to teach the church today.