ROME — Retired Pope Benedict XVI has broken his silence to reaffirm the “necessity” of priestly celibacy, co-authoring a bombshell book at the precise moment that Pope Francis is weighing whether to allow married men to be ordained to address the Catholic priest shortage.

Benedict wrote the book, From the Depths of Our Hearts: Priesthood, Celibacy and the Crisis of the Catholic Church, along with his fellow conservative, Guinean Cardinal Robert Sarah, who heads the Vatican’s liturgy office and has been a quiet critic of Francis.

The French daily Le Figaro published excerpts of the book late Sunday; The Associated Press obtained galleys of the English edition, which is being published by Ignatius Press.

Benedict’s intervention is extraordinary, given he had promised to remain “hidden from the world” when he retired in 2013, and pledged his obedience to the new pope. He has largely held to that pledge, though he penned an odd essay last year on the sexual abuse scandal that blamed the crisis on the sexual revolution of the 1960s.

His reaffirmation of priestly celibacy, however, gets to the heart of a fraught policy issue that Francis is expected to weigh in on in the coming weeks, and could well be considered a public attempt by the former pope to sway the thinking of the current one.

The implications for such an intervention are grave, given the current opposition to Francis by conservatives and traditionalists nostalgic for Benedict’s orthodoxy, some of whom even consider his resignation illegitimate.

It is likely to fuel renewed anxiety about the wisdom of Benedict’s decision to remain an “emeritus pope,” rather than merely a retired bishop, and the unprecedented situation he created by having two popes, one retired and one reigning, living side by side in the Vatican gardens.

In that light, it is significant that the English edition of the book lists the author as “Benedict XVI,” with no mention of his emeritus papal status on the cover.

The authors clearly anticipated the potential interpretation of their book as criticism of the current pope, and stressed in their joint introduction that they were penning it “in a spirit of filial obedience, to Pope Francis.” But they also said that the current “crisis” in the Church required them not to remain silent.

Francis has said he would write a document based on the outcome of the October 2019 synod of bishops on the Amazon. A majority of bishops at the meeting called for the ordination of married men to address the priest shortage in the Amazon, where the faithful can go months without having a Mass.

Francis has expressed sympathy with the Amazonian plight. While he has long reaffirmed the gift of a celibate priesthood in the Latin rite church, he has stressed that celibacy is a tradition, not doctrine, and therefore can change, and that there could be pastoral reasons to allow for an exception in a particular place.

Benedict addresses the issue head-on in his chapter in the brief book, which is composed of a joint introduction and conclusion penned by Benedict and Sarah, and then a chapter apiece in between. True to his theological form, Benedict’s chapter is dense with biblical references and he explains in scholarly terms what he says is the “necessary” foundation for the celibate priesthood that dates from the times of the apostles.

“The priesthood of Jesus Christ causes us to enter into a life that consists of becoming one with him and renouncing all that belongs only to us,” he writes. “For priests, this is the foundation of the necessity of celibacy but also of liturgical prayer, meditation on the Word of God and the renunciation of material goods.”

Marriage, he writes, requires man to give himself totally to his family. “Since serving the Lord likewise requires the total gift of a man, it does not seem possible to carry on the two vocations simultaneously. Thus, the ability to renounce marriage so as to place oneself totally at the Lord’s disposition became a criterion for priestly ministry.”

The joint conclusion of the book makes the case even stronger, acknowledging the crisis of the Catholic priesthood that it says has been “wounded by the revelation of so many scandals, disconcerted by the constant questioning of their consecrated celibacy.”

Dedicating the book to priests of the world, the two authors urge them to persevere, and for all faithful to hold firm and support them in their celibate ministry.

“It is urgent and necessary for everyone—bishops, priests and lay people—to stop letting themselves be intimidated by the wrong-headed pleas, the theatrical productions, the diabolical lies and the fashionable errors that try to put down priestly celibacy,” they write. “It is urgent and necessary for everyone—bishops, priests and lay people—to take a fresh look with the eyes of faith at the Church and at priestly celibacy which protects her mystery.”

The book is being published at a moment of renewed interest — and confusion — in popular culture about the nature of the relationship between Francis and Benedict, thanks to the Netflix drama, “The Two Popes.”

The film, starring Anthony Hopkins as Benedict and Jonathan Pryce as Francis, imagines a days-long conversation between the two men before Benedict announced his historic resignation — conversations in which their different views of the state of the Church become apparent.

Those meetings never happened, and the two men didn’t know one another well before Francis was elected to succeed Benedict. But while the film takes artistic liberties for the sake of narrative, it gets the point across that Francis and Benedict indeed have very different points of view — which the new book bears out.

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