The pope is by far the world'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 world leaders.
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.
The pontiff leads about 1.1 billion Catholics worldwide, comprising about 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, the pope alone can set the direction and tone for the church.
Yet, as a growing number of Europeans and Americans from different faiths leave organized religion, many Christians have welcomed the pope's prominence as a much-needed voice for traditional belief.
Monday, when the pope announced his 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. 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.
“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.
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.