The sexual abuse of children by those who have vowed to serve Christ and the church is a horrendous monstrosity that represents "a diabolical sacrifice" of innocent, defenseless lives, Pope Francis said.

The Church, which must protect the weakest, has a duty "to act with extreme severity with priests who betray their mission and with the hierarchy -- bishops and cardinals -- who protect them," the Pope wrote in the preface to a new book written by a man raped as a child by a Capuchin priest.

The book, My Father, I Forgive You (Mon Pere, Je Vous Pardonne), was written by Daniel Pittet, 57, in an effort to describe how he fell victim to a predator abuser when he was 8 years old growing up in Fribourg, Switzerland, and the challenges he faced when came forward two decades later with the accusations. The book, currently published only in French, was to be released on February 16. News outlets released the text of the Pope's preface on February 13.