VATICAN CITY - The act of resigning will be one of the most enduring legacies of Pope Benedict XVI.
As the first pope in 600 years to step down, Benedict shocked the world Monday. Yet in so doing, the conservative pope made a progressive statement that the head of the world's 1.2 billion Roman Catholics must be energetic enough to engage forcefully in the moral battles of the modern world, theologians and Vatican watchers say.
It was "the most modernizing decision Pope Benedict has taken," said Michael Sean Winters, a National Catholic Reporter columnist. "In a single moment, the pope has removed some of the aura of the papacy."
Theologian George Weigel called the pope's resignation a "great act of humility and self-abnegation" that looks to improving the future of the church under a new, vigorous pope. "He wants the church to be well served," as it faces immense demands, he said.
During his eight years as pope, Benedict, 85, picked up where his predecessor and friend Pope John Paul II left off by standing fast for core Christian values such as a respect for traditional marriage.
He insisted on adherence to Catholic precepts for Catholic universities and religious orders, oversaw the return of the Mass to more historical roots, and urged secular leaders to follow Christian teachings on morality in their decisions.
Citing age and declining health, Benedict announced in Latin during a meeting of cardinals that he would resign as of Feb. 28. A conclave of cardinals will elect a successor next month. Federico Lombardi, a Vatican spokesman, said he expected a new pope before Easter.
"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths due to an advanced age are no longer suited" for the task, Benedict said. "Both strength of mind and body are necessary, strengths which in the last few months have deteriorated in me to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me."
John Paul II was a broad-shouldered sportsman of 58 when he was elected pope in 1978. Benedict was already frail when he was elected at the age of 78, the oldest man elevated to pope since Clement XII in 1730.
And while the charismatic John Paul wowed crowds in St. Peter's Square, the shy Benedict usually opted for public audiences that prompted contemplation among the faithful.
Theologians say it is difficult to predict whom the College of Cardinals will choose as the new pope, though the church is facing a number of challenges that might affect the papal conclave's decision.
John Murray, a lecturer in moral theology at the Mater Dei Institute of Education in Dublin, said the German-born Benedict, formerly Cardinal Joseph Ratzinger, was chosen in part to address rising secularism in Western Europe. "That's still a challenge obviously," he said.
As church attendance in Western Europe declines and fewer men and women enter religious orders, the new pope may come from a developing country in Africa, Latin America or Asia where the church is thriving. Still, many analysts expect continuity similar to Benedict's selection.
"Ratzinger very much followed John Paul, worked for John Paul, so will the next person be of the same mind with those two previous popes?" said Garry O'Sullivan, editor of The Irish Catholic newspaper.
Or will a new pope have to confront new challenges with new policies? "These are tumultuous times," said Brennan Pursell, author of the biography, Benedict of Bavaria: An Intimate Portrait of the Pope and His Homeland. "You have a society that is rapidly separating itself from its cultural and social roots to the church."
Africa, South and Central America and Asia are likely to take more focus. Church positions that some Western Catholics take issue with - on contraception, divorce, homosexuality - are not of pressing importance in those parts of the world.
Regardless, no one expects big changes at the church's core values. Benedict approved the appointment of the majority of the church's cardinals, so there won't be reversals on views of homosexuality, women's ordination or abortion, observers say.
"It's the pope's job to stand at the helm, never change its credo," Pursell said. "Adjustments have to be made every day, in every age. But all popes are conservative. It is their job to be conservative, to preserve the Catholic Church."
Though a staunch conservative when it came to church teachings, Benedict has recognized the importance of keeping Christianity relevant to the modern world.
He tweets from an iPad, beams benedictions from a Facebook page and distributes Vatican news from a YouTube channel.
The scholarly pontiff
As a cardinal, he was a mighty theologian known for his scholarship.
Among his accomplishments:
He presided over the restoration of the Mass to historic richness by drawing the prayers said and sung closer to their ancient Latin roots.
He appointed orthodox - and media savvy - bishops and cardinals to steer the church for years to come. His appointees now outnumber John Paul's in the College of Cardinals. Catholic liberals griped that his appointments were not as concerned about the church's historic stands for social justice as the liberals wanted.
He stepped up dialogue with the Eastern Orthodox across centuries-old divisions. He raised Catholic-Jewish relations to "unprecedented levels by speaking out against Holocaust denial, World Jewish Congress President Ronald Lauder said.
He issued three encyclicals on love and charity including a strong call for a "establishing a true world political authority" with "real teeth" to manage the global economy with God-centered ethics to bring economic justice to the world's poor.
He campaigned for a "New Evangelism" to combat the trend toward secular lifestyles. The focus was on converting baptized Catholics to a deeper, more vital faith.
He aimed the campaign at Europe, where Mass attendance was below 10%; North America, where millions of Catholics are not living by church teachings, and South America, where thriving Protestant missions encroach on the flock.
He was no globe-trotter like John Paul II, but crowds were enthusiastic on his 25 trips outside Italy. At home, he drew more to the weekly audience in St. Peter's Square than his predecessor. Soon, says theologian Weigel, there was a saying in Rome: "People came to see John Paul; they come to hear Benedict."
The job of leading in preaching, teaching and governing the world's largest non-governmental organization in enormous. The church had a pastoral pope in John Paul, followed by a deep scholar in Benedict. Is it time for a manager to bring professionalism to the vast machinery?
"We need all three," said James Martin, culture editor of the Jesuit magazine America.
No surprise for brother
The pope's brother, Georg Ratzinger, said Monday he had known for months the resignation was coming. By 2011, the arthritic pope was using a cane, the Vatican said. At Christmas services last year, he was stooped, his eyes half closed, his face haggard.
Pursell believes Benedict resigned to tell successors they need not remain in the Vatican if they cannot bring to the position all it requires.
"To serve the church you have to have all your power," Pursell said. "He intentionally established a new principle for the post-modern world: Why should a pope stay in office if he doesn't choose to."
Still, some Catholics were shocked and felt Benedict should have stayed on. John Paul survived two assassination attempts and was diagnosed with Parkinson's disease four years before he died in office. His appearances in public were seen by many as his way of showing the faithful that we possess human dignity and worth no matter our years.
"I am quite surprised that he is resigning," said retiree Carla Pensato, 65, in Rome. "It seems weird that a great theologian like him would resign just because he's exhausted."
Murray said Benedict's announcement came as a surprise initially but recalled statements Benedict made indicating "he was opening the door to the possibility" for popes to step down when John Paul II's health was declining preceding his death in 2005.
"John Paul was a very fine witness to suffering in old age, and the way he held on until the very end was a real inspiration to us all - and in a way there was no need for anyone else to do that again," he said. "Benedict plans to go and pray and live out his life quietly. It is a very humble thing to do. He is showing us that nobody is indispensable."
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