VATICAN CITY — Retired Pope Benedict XVI has broken his silence to reaffirm the value 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, 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, and are likely to fuel renewed anxiety about the unprecedented situation of two popes, one retired and one reigning, living side by side in the Vatican gardens.

The authors clearly anticipated that potential interpretation, and stressed in their joint introduction that they were penning the book “in a spirit of filial obedience, to Pope Francis."

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On Monday, the Vatican press office put out a statement affirming Pope Francis's commitment to celibacy and pointing out his recent statements on the topic.

"The position of the Holy Father on the issue of celibacy is well known," said read the statement.

"Personally I think that celibacy is a gift for the Church. I do not agree with allowing celibacy as an option, no. This could be a possibility only in the most remote of areas — I think of the islands in the Pacific ocean — where there are priesthood needs. Priests need to think of the faithful," the statement quoted the pope as saying on a recent flight from Panama.

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 a 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.