Benedict, who still lives in the Vatican and is failing health, has defended priestly celibacy in the book written jointly with a conservative cardinal in what appears to be a strategically timed appeal to Pope Francis to keep a hard line.
In a series of tweets published January 12, Kurt Martens, a professor of canon law at the Catholic University of America, said he looked forward to reading the book, but stressed the need "to recall that there is only one Pope, one Bishop of Rome: Francis".
He said: "It doesn't seem possible to realise both vocations (priesthood and marriage) simultaneously".
While Francis has not ruled out a limited change in a specific region, he has also strongly supported priestly celibacy in general.
The 92-year-old German became the first pope to resign in nearly 600 years when he stepped down in 2013.
The Vatican told CNN on Monday that it was not now commenting on the matter.
Benedict's chapter examines the history of the priesthood in the Old and New Testaments, saying that a proper understanding of the nature of the priesthood is crucial in answering contemporary questions about priestly celibacy.
"It was a misunderstanding, without putting into doubt the good faith of Cardinal Sarah", Gaenswein said in the statement published by Vatican News.
Just two hours later, during a day of fast-paced drama in the Vatican, the cardinal issued a follow-up tweet to announce that Benedict's name would be removed as a co-author, and he would be listed as a contributor instead.
The cardinal tweeted a photo of a letter dated November 25 in which Pope Benedict thanked him "for the text added to my contribution and for the whole elaboration you have done".
James Martin, a Jesuit priest and editor of the Catholic publication "America", said he feared a "parallel magisterium, which can lead to disunity".
Vatican commentators have, however, expressed surprise with the retired pope's intervention.
The retired Pope also acknowledged that the Catholic priesthood has been "wounded by the revelation of so many scandals, disconcerted by the constant questioning of their consecrated celibacy". 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.
"Benedict XVI and Cardinal Sarah have written an eloquent defense of celibacy, not an attack on Pope Francis", he said in a tweet.
'No-one is doubting that Benedict agrees with the premise of the book - to retain clerical celibacy for the Latin rite priesthood, ' said Vatican expert Christopher Lamb.
A majority of bishops at the synod in October said married men should be ordained to offer a supply for the shortage of priests.
Moreover, Vatican News recalls that Benedict XVI himself allowed for certain exceptions to the rule, notably in admitting married Anglican priests who seek communion with the Catholic Church to be ordained as Catholic priests "on a case by case basis". "However, the full text remains absolutely unchanged", he said.
Catholic social media was abuzz Monday after Benedict's bombshell, with Francis' supporters saying it showed the problems of having an "emeritus pope" seemingly undermining the current pope, and suggesting that Benedict - at age 92 and increasingly feeble - was being manipulated by his conservative entourage.
"It's about the freedom of one pope Francis AND of the synodal process".
"One pope is complicated enough".
By his intervention, Cardinal Robert Sarah has only fulfilled his grave duty and proven to have been a true help to the Pope and, in this manner, to the entire Church.
"I'm not in agreement with allowing optional celibacy", he said.
"There could only be a possibility in these far, far away places, I think about the islands in the Pacific, but it's something to think about, when there's a pastoral need, there the shepherd has to think about the faithful".