Retired Pope Benedict XVI has issued a defence of priestly celibacy in the Catholic Church as his successor considers easing a ban on married men serving as priests.
Pope Benedict made the appeal in a book co-authored with Cardinal Robert Sarah.
It comes in response to a proposal to allow married men to be ordained as priests in the Amazon region.
Pope Benedict, who retired in 2013, said he could not remain silent on the issue.
In the book, Pope Benedict says celibacy, a centuries-old tradition within the Church, has “great significance” because it allows priests to focus on their duties.
The 92-year-old says “it doesn’t seem possible to realise both vocations [priesthood and marriage] simultaneously”.
It is rare for Pope Benedict, who was the first pontiff to resign in almost 600 years, to intervene in clerical matters.
The Vatican is yet to comment on the book, which was previewed in part by French newspaper Le Figaro before its full publication on Monday.
When Benedict resigned in 2013, he promised “unconditional reverence and obedience” to his successor.
Massimo Faggioli, a theologian at Villanova University in the US, tweeted: “Benedict XVI is really not breaking his silence because he (and his entourage) never felt bound to that promise. But this is a serious breach.”
He added that “for some Catholics, Benedict XVI never retired really”.
Celibacy became a tradition in the church about 1,000 years ago.
Relaxation of the rules in the Amazon, where Catholics can wait months for their next Mass, would apply to older men who are already deacons in the church, have a stable family life and have shown leadership in their communities.
The idea was put forward at an assembly of bishops in October. Francis is due to comment on the matter in the next few months.
When Benedict became the first pope to resign in 700 years, he said he would remain “hidden from the world”.