PARIS (Reuters) - It's rare to be invited to an event five years off and even rarer to bicker about its details, but Germany's Catholic Church finds itself in that delicate situation thanks to an overture from its Protestant neighbors.
German Protestants are planning jubilee celebrations in 2017 to mark the 500th anniversary of Martin Luther's launching of the Reformation, a major event in the history of Christianity, of Europe and of the German nation, language and culture.
The Protestants have invited the Catholics to join in, a gesture in harmony with the good relations the two halves of German Christianity enjoy and the closeness many believers feel across the denominational divide.
But even after five centuries, being asked to commemorate a divorce that split western Christianity and led to many bloody religious wars is still hard for some Catholics to swallow.
"It's not impossible in principle, but it depends on the character of the events planned," Bishop Gerhard Feige, the top Catholic official dealing with Protestants, said in a statement for the Protestant Reformation Day holiday on Wednesday.
"Catholic Christians consider the division of the western Church as a tragedy and - at least until now - do not think they can celebrate this merrily," he wrote in the text outlining Catholic doubts about the event.
The Reformation began in 1517 when German monk Martin Luther nailed his 95 Theses to a church door to denounce corruption in the Catholic Church, especially the sale of indulgences to help build the lavish new Saint Peter's Basilica in Rome.
Excommunicated by Rome, he won support from German princes who soon battled others who remained Catholic. The ensuing wars of religion killed about a third of Germany's population over the next century and spread to neighboring countries as well.
After Luther's break with Rome, dissent spread and thousands of new denominations eventually emerged, the largest being the Presbyterians, Anglicans, Baptists, Methodists and Lutherans.
Luther is also a major cultural figure in Germany thanks to his pioneering translation of the Bible, which shaped the German language as much as Shakespeare's plays influenced English.
Commemorative church services, concerts and conferences leading up to 2017 are already underway around Germany. There are also cultural events, such as a show of 800 plastic statues of Luther that filled the main square in Wittenberg in 2010.
This mix of religious, cultural and commercial activities led Feige to ask what the Catholics were being invited to join.
"Many initiatives and plans may well be justified, but it's not always easy to find out what 2017 will be all about," he wrote in what he called his "Ten Catholic Theses".
"It would be good if the Protestants would work out some points more clearly," he said.
Catholic-Protestant cooperation is a public issue in Germany, where the churches are equal in size and active in public life. Both run many schools and social services.
Intermarriage between Catholics and Protestants is common.
Prominent politicians from right and left recently issued a manifesto urging more progress towards overcoming their split.
While many Germans stress the similarities between the two, the churches remain quite distinct.
Catholicism is centralized under the Vatican in Rome and its teachings tend to be more conservative, while the Protestants are split into many local churches that range from conservative to liberal but value their freedom to govern themselves.
Feige said Catholics and Protestants had come closer to each other since the 16th century, especially since the reforms of the 1962-1965 Second Vatican Council opened the Catholic Church to more contact with other faiths.
But there were still major differences between them on issues such as the office of the pope, the meaning of the eucharist and the role of the priest that could not be ignored.
Feige also found some Protestant depictions of the Reformation too positive, playing down the suffering and divisions it caused over the following centuries.
"It would be very helpful if both denominations could come to a common understanding of what happened," he said, suggesting they could find some way to "cleanse their memories".
Margot Kaessmann, a former Lutheran bishop who heads the preparations for the 2017 events, has said she wants Catholics to join in but turned down a Vatican suggestion both sides work out a common admission of guilt for the separation.
The Evangelical Church in Germany (EKD), the main Protestant federation, plans to discuss the preparations for 2017 at its annual synod meeting next week.
Editing by Jon Boyle