's most visible religious figure. His office can be a bully pulpit on everything from salvation to the economy. In his overseas travels, he's greeted with the kind of pomp and reverence accorded major world leaders.
But as Pope Benedict XVI prepares to step down, questions are being raised about just how influential his successor can be. He will be taking command of a church that has been weakened in recent decades — by rising secularism in the West, fallout from clergy sex abuse, competition from Pentecostal groups in the developing world and crises within the Vatican itself.
"Many Catholics, particularly in the Western world, take the pope's counsel seriously, but they don't consider it binding," said Mathew Schmalz, a professor who specializes in global Catholicism at College of the Holy Cross in Worcester, Mass. "But since we live in an age of technology and 24-hour media, the symbolic influence has increased. Benedict recognized this, that you need someone who is healthy and robust to engage this complex environment."
No other religious group has invested a leader with as much organizational authority and reach as the Catholic pope.
The pontiff leads about 1.1 billion parishioners worldwide, comprising around one-half of the globe's Christian population, according to a 2011 study by the Pew Forum on Religion & Public Life. While he is bound in many ways by precedent and history, he alone can set the direction and tone for the church. Until relatively recently, these powers were a central theme of anti-Catholic hatred. (John F. Kennedy, the first Catholic U.S. president, famously pledged his administration wouldn't take orders from the Holy See.)
Yet, as a growing number of Europeans and Americans from different faith traditions leave organized religion, many Christians have welcomed the pope's prominence as a much-needed voice for traditional belief. On Monday, when the pope announced his stunning decision to resign, the Rev. Albert Mohler, president of the flagship seminary for the evangelical Southern Baptist Convention, tweeted: "Remember that millions of people around the world gain their idea of what Christianity is from the papacy."
The rise in technology has been a double-edged sword for the church. Young people trying to decide whether to remain Catholic have access to more arguments than ever about why they should leave. But at the same time, technology has built a greater intimacy between the pontiff and the public. Compared to many evangelical groups, the Catholic church was slower to take advantage of the Internet. But the pope is now on Twitter. His statements are posted in several languages at once. Papal events are broadcast on the Web.
"They have a backstage pass to the Vatican," said David Kinnaman, president of the Barna research group and author of "You Lost Me" and other books about young Christians and religion. "It gives both the perception and reality of access that previous generations might not have had."
Still, at least in the West, the pope is advancing these views in a modern world less open to hearing them. Gay relationships are gaining acceptance even among many theologically conservative American and European Christians. Women are taking more prominent positions of authority in all spheres of life, keeping the church on the defensive about the all-male priesthood. The church ban on artificial contraception is at the heart of a fight by Catholic bishops against a requirement in President Barack Obama's health care overhaul that workers' insurance covers birth control.
"I think for a lot of young people, the cultural argument is already settled, so there's a lot of tension there," said Dennis Doyle, a University of Dayton professor who specializes in the Catholic church. "We can't simply label these issues in terms of sin and temptation."
Yet, while the church is shrinking in the West, it is growing dramatically in Africa and other parts of the developing world, where Christianity tends to be more theologically conservative and more in step with papal teaching. Pentecostal churches are drawing some parishioners away. Still, by 2025, almost half of all Catholics will be in Latin America, Africa and Asia, said Juan Martinez, a Latino studies professor at Fuller Theological Seminary, an evangelical school in Pasadena, Calif. The average Catholic will be a relatively poor, young mother from Brazil, the Philippines or sub-Saharan Africa.
"Her issues and what she expects and how she defines her faith and what she expects from the church in her walk of faith, look extremely different," Martinez said.
Mark Noll, a scholar of evangelical history at the University of Notre Dame, argued it would be wrong to view the papacy as weakened because of the challenges before the church. Given the splits within Protestantism and among secular-minded people, few leaders have the platform a pope does.
"The papacy remains the world's oldest continual functioning institution," Noll said. "There is a tremendous proliferation of voices in the world. Nonetheless, you have this historical institution that becomes rare and rarer."