While affecting Catholics and Protestants everywhere, however, the anniversary will be centered on nearby Germany, where the Reformation's founder, Martin Luther (1483-1546), launched his rebellion against Rome in the early 16th century.
"The Reformation still causes real division here -- even today, despite all efforts to bring people together, it poses problems in parts of our society," Thomas Lazar, a spokesman for Germany's Catholic church, told NCR. "For all our recent achievements in coexistence and co-operation, closer ties are still needed between us. I hope Protestants will appreciate the effort Catholics are making for this event."
Francis will attend a Catholic-Lutheran prayer service on Oct. 31 at the Protestant cathedral of Lund in southern Sweden. It will mark the start of yearlong commemorations of the Reformation, which is traditionally dated from the October 1517 publication of Luther's "Ninety-Five Theses," which questioned the sale of indulgences and the Gospel foundations of papal authority.
In a joint statement this June, the Vatican's Pontifical Council for Promoting Christian Unity and the Geneva-based Lutheran World Federation said the pope's visit would also include a 10,000-strong arena gathering at nearby Malmo to "celebrate the fruits of 50 years of dialogue."
Even in Scandinavia, planning for the event has sparked controversy.
Last April, Catholic Bishop Czeslaw Kozon, president of the Nordic Bishops' Conference, complained about a lack of consultation, and cautioned that local Catholics would "show little interest" if the papal visit was confined to contacts with Lutherans.
Catholic teaching is attracting new interest at a time when Scandinavia's predominant Lutheran churches have adopted "very liberal positions," warned Kozon, who heads the diocese of Copenhagen, Denmark. So this was not a time for the Catholic church to be keeping a low profile.
Plans for a Catholic Mass at Malmo will have allayed some of the misgivings, while the Nordic Bishops' Conference is to issue a pastoral letter in the run-up to the pope's arrival, urging local Catholics "to reflect and repent for the wound of separation."
Yet with views and perspectives still far apart in some quarters, further efforts will be required to ensure the anniversary passes peacefully.
"There's disappointment in Germany the pope isn't coming here too, although this was never seriously anticipated," Lazar explained. "And while there's no doubt our mutual understanding is much better now, thanks to the work of recent decades, it'll still be important to look back at what we did to each other and seek forgiveness."
Luther's famous "Theses," pasted on his church door at Wittenberg in Saxony and sent to the Catholic archbishop of Mainz, denounced the new practice of indulgences and claims that the pope held power in purgatory. His objections soon broadened into a wider critique of papal authority -- and an insistence that the Bible held primacy and salvation was attained by faith alone.
Over the following four years, Luther produced works doubting Catholic devotions to the Virgin Mary and the intercession of saints, and questioning the sacraments, good works, clerical celibacy, monasticism, church law and excommunication, as well as the role of secular rulers in religious affairs.
While his key motivation was theological, his reform drive acquired political overtones, forcing Germany's princes to decide whether to stay loyal to the pope or pitch in behind new Protestantism. It was hardly surprising that while Luther was excommunicated by Pope Leo X in 1521, he was also outlawed by Holy Roman Emperor Charles V.
Yet Luther's movement diversified as the Bible and other Christian texts were printed in local languages, and soon became divided between Luther's followers and those of Huldrych Zwingli and John Calvin in neighboring Switzerland. Radical offshoots emerged, including the Moravians and Anabaptists, sparking the German Peasants' War, in which at least 100,000 died.
The Catholic church responded with a Counter-Reformation, initiated by the 1545-63 Council of Trent and led in part by the new Society of Jesus.
But Lutheran churches were founded in Germany, the Baltic states and Scandinavia, and Reformed or Calvinist churches in Switzerland, Hungary, France, the Netherlands and Scotland, while a separate Church of England, formed under King Henry VIII, attempted a via media, or middle way, combining Protestant liturgy and administration with a Catholic priesthood and sacraments.
The clash of ideas and influences spurred the advance of literacy, state administration and economic development. While Northern Europe mostly opted for Protestantism, and Southern Europe remained Catholic, much of Central Europe was devastated over the next century by religious wars, as Catholic and Protestant rulers fought and allied against each other.
Signs of rapprochement
Not surprisingly, the Reformation left deep rifts and resentments, and it was only at the 1962-65 Second Vatican Council that real signs of rapprochement began to appear.
Vatican II's November 1964 Decree on Ecumenism, Unitatis Redintegratio, conceded that the continued division "openly contradicts the will of Christ, scandalizes the world and damages the holy cause of preaching the Gospel." It urged Catholics to "recognize the signs of the times" and work for ecumenical ties, and called for dialogue on issues such as ministry, authority and worship.
Three decades later, Pope John Paul II's 1995 encyclical Ut Unum Sint also appealed for a "clearer understanding" of the Eucharist, ordination and Catholic magisterium, as well as the intercessory role of the Virgin Mary and the relationship between Scripture and tradition.
In 1999, a historic Catholic-Lutheran joint declaration concluded that both churches could now "articulate a common understanding" of the key Reformation doctrine of justification, and confirmed that "remaining differences" no longer merited condemnations.
Aided by new insights, the Joint Declaration on the Doctrine of Justification enthused, it was now possible "to formulate a consensus on basic truths." A "decisive step forward" had been taken "on the way to overcoming the division of the church."
Less than a year later, a declaration from the Vatican's Congregation for the Doctrine of Faith called Dominus Iesus enraged Lutherans by appearing to relegate non-Catholic churches to the status of "ecclesial communities," lacking the "fullness of the means of salvation."
Yet key subsequent statements to Lutheran leaders -- by Pope Benedict XVI in Erfurt, Germany, in September 2011, and Pope Francis in Rome in December 2014 -- have confirmed closer ties. It's been in Germany, the Reformation's heartland, where the most marked progress has been achieved.
Catholics make up 29 percent of Germany's 82 million inhabitants; members of 15 regional Lutheran churches of the Evangelical Church of Germany make up 27 percent. While both have faced declining membership, they've also cited a growing closeness.
Back in 1980, one joint report described the 1530 Augsburg Confession, which set out the new Lutheran faith, as "worthy in intention" and confirmed that Catholics and Lutherans could now "see Jesus Christ together as the living center of their faith."
In 1983, on the 500th anniversary of Luther's birth, another joint Catholic-Lutheran document praised the reformer as "witness of the Gospel, teacher in faith and summoner to spiritual renewal."
Another in 1986 asked whether Reformation-era church leaders had "correctly understood" convictions at the time, while a shared report in 1996 recognized that Luther's "understanding of the Word of God" could serve as "a role model for all Christians."
This August, the German Bishops' Conference made another major gesture by bringing key ecumenical documents since the 1960s together in a 206-page collection, and explaining how each had contributed to closer ties.
In his foreword, Magdeburg Bishop Gerhard Feige, chairman of the German church's Ecumenical Commission, confirmed the "common judgement" that previous condemnations were now invalid, and predicted the collection would help Catholics and Lutherans come together behind joint "development goals."
"The history of the Reformation has, over time, encountered a changeable reception in the Catholic church, where its events and protagonists were long seen in a negative, derogatory light -- through a long ecumenical dialogue, the theological differences rooted in the period have been re-evaluated," Feige added.
"Memories of the Reformation and subsequent separation of Western Christianity are still not free from pain. But while wounds are still felt to the present day, it's gratifying that Catholic theology has succeeded, in the meantime, in soberly reconsidering these 16th-century events."
In their overall introduction, the German bishops went further still, bringing Catholics closer to endorsing some of the Reformation's claims. Luther's work still posed a "theological and spiritual challenge," they noted, and had "ecclesial and political implications for understanding the church and its magisterium."
However, Luther himself should now be seen as "a religious pathfinder, Gospel witness and teacher of the faith," whose "concern for renewal in repentance and conversion" had not been given an "adequate hearing" by Rome.
"The Catholic church may recognize today what was important in the Reformation -- namely, that sacred Scripture is the center and standard for all Christian life," the bishops confirmed.
"Connected with this is Martin Luther's fundamental insight that God's self-revelation in Jesus Christ for the salvation of the people is proclaimed in the Gospel -- that Jesus Christ is the center of Scripture and the only mediator."
'A basic duty'
Conservative Catholics have long complained about the liberal stance taken by German bishops on aspects of Catholic teaching, a contention that was showcased at the October 2015 Synod of Bishops on the family. Those Catholics may well see the favorable evaluation of Luther's reforms as a new provocation.
But Fulda Bishop Heinz Josef Algermissen, the Ecumenical Commission's vice-chairman, is optimistic.
"Ecumenism has to be considered a basic duty for Christians -- if we confess one church, we have to make an effort and pray for the restoration of broken unity," Algermissen, who also heads the German church's Pax Christi association, told NCR. "We have a common responsibility for our faithful -- and this includes a commitment to peace, to the persecuted and to refugees. We also have to find a common voice in protecting human life against abortion and euthanasia, as well as on other vital bioethical matters."
Besides the Swedish ceremonies with the pope, anniversary commemorations are planned in Wittenberg, Halle and other towns linked to Luther's movement.
In an exchange of conciliatory letters in June 2015, the German Bishops' Conference president, Cardinal Reinhard Marx, and the Evangelical Church in Germany president, Bishop Heinrich Bedford-Strohm, outlined plans for a joint Catholic-Lutheran message "witnessing to the hope that defines us as Christians" -- to be issued during an unprecedented ecumenical pilgrimage to the Holy Land.
A service for "healing memories" is also planned for Lent 2017, as well as a major interchurch conference on the Bible, to express what Marx has called the "deep mutual connection formed through faith in Jesus Christ, the reading of Scripture and the sacramental bond of baptism."
Other fixtures will include ecumenical ceremonies for the Exaltation of the Cross, known by Lutherans as Holy Cross Day, and a joint "missionary jet force" to re-publicize the Christian faith in German society.
"The Reformation and developments that followed it are also a part of Catholic church history," Marx told Bedford-Strohm in his letter. "In Germany, where the Reformation originated, we have a special joint responsibility to ensure this act of remembrance strengthens the rapprochement between our churches."
Lazar, the German church spokesman, thinks most Catholics and Lutherans will concur in using the anniversary as an opportunity to come closer than ever before, and to reveal Christianity's vitality to a secularized country where it's long been in retreat.
Algermissen agrees. While much remains to be done, he's sure the shared commemoration will "provide a bold impulse" for "speaking with one voice as Christians," while also encouraging Catholics to reflect on the tragic divisions from the past.
"We must ask ourselves whether the Reformation was really an event breaking with the past, or actually something in continuity with a universal church tradition," Algermissen told NCR. "In any event, we can't just see this as a jubilee. We must also contemplate the errors of the past, admitting our guilt and repenting on both sides for the past 500 years. And we must aim not just at reconciled diversity, but at visible unity."