The movie The Two Popes is a largely fictional account of the doctrinal differences between the retired Pope Benedict XVI and Pope Francis.

In real life, those differences were brought to the surface this week when retired Benedict issued a strongly-worded defense for priestly celibacy — countering his successor Pope Francis, who has publicly affirmed this tradition of the Roman rite, but who is also considering allowing older married men to be ordained in the Amazon to deal with a shortage in that part of the world.

The pope emeritus made the surprise comments in a book, excerpts of which were printed in the French newspaper Le Figaro, co-authored with Cardinal Robert Sarah (click here for the cardinal’s defense of listing the retired pope as an author of materials in the book).

What journalists covering this ongoing story need to focus on is explaining what it means for a pope to be infallible on matters of doctrine, as talk of schism intensifies. Also, what role does an emeritus pope play? What does clergy celibacy mean doctrinally for Catholicism? All of these factors will have a bearing on what Pope Francis ultimately decides to do regarding doing away with celibacy among men serving congregations in the Amazon region.

Both Benedict and Sarah are doctrinally conservative, while Francis is widely seen — especially in media reports — as a progressive who wants to change many church teachings to deal with changes in the modern world.

In the book, titled "From the Depths of Our Hearts,” the 92-year-old Benedict makes the case in favor of the centuries-old tradition of celibacy, saying it allows men to “put oneself completely at the disposition of the Lord.”

The celibacy requirement, Benedict argues in his chapter in the book, is “truly essential” and should not be lifted.

"The call to follow Jesus is not possible without this sign of freedom and of renunciation of all commitments," he wrote. “Celibacy must penetrate, with its requirements, all of the attitudes of existence.”

The English edition of the book is scheduled to be released next month.

Benedict’s comments come three months after Pope Francis held a three-week synod on the issues plaguing the Amazon region. The October meeting’s recommendations, which included allowing married men to be ordained, raised concerns among conservative Catholics.

The ordination of married men, even if Pope Francis accepts the proposal, would call for the elaboration of a new “Amazonian rite,” reflecting the unique situation in that part of the world. It’s not meant to be used in other parts of the world. Married men have, for centuries, been ordained as priests in Eastern Catholic Rites and in a few other circumstances, such as former Anglican priests entering Roman Catholicism.

The 31-page final synod document, which was voted upon by those participating, called for “esteemed men of the community” to be allowed to serve as priests. Pope Francis is expected to make a decision on the matter sometime this year.

In response to Benedict, Vatican spokesman Matteo Bruni told reporters: “The position of the Holy Father on celibacy is known,” quoting the pope's comments to journalists made last year.

But Bruni also included 83-year-old Francis' statement that "some possibility" could exist for exceptions regarding ordinations in the Latin Rite in order to accommodate remote parts of the world. Critics of such a measure have argued that it could open the door for married clergy in North America and Europe, where vocations are down sharply.

It should be noted that Benedict is no longer pope — Francis is.

What does that mean in terms of doctrine?

It means that while Benedict XVI remains part of the Vatican’s hierarchy, he is no longer infallible on matters of faith. That responsibility belongs to Francis, who was elected in 2013 after Benedict made the unusual decision to step down.

For example, after resigning, Benedict publicly pledged to the College of Cardinals that he would accept and obey whomever they elect as his successor. To some Catholics, and journalists, it now appears as if Benedict has broken that vow.

What comes next could divide the church even further — even end in a schism — or force Francis to leave things as is in order to avoid further division.

Either way, Benedict isn’t gone. Instead, he’s exerting influence at a time when the church is fractured and in need of healing. How Francis responds in the coming days and weeks remains to be seen.

For this pontiff, it’s already been a busy year. Thanks to Benedict, it just got busier — and more fragmented.