Benedict returned to his native Germany for the third time since becoming pope in 2005, but it was his first official state visit and the first time he had ever addressed the Bundestag.

Those expecting a contentious speech may have been disappointed. In comments that verged at times on the academic, the theologian pope spoke about the importance of responsibility of political leaders, and touched on several themes at the heart of his papacy: the fight against secularism and relativism. He also called for opening a debate on ethics.

Among the leading voices opposing his appearance came from the Green Party, which Benedict singled out for praise. "The emergence of the ecological movement in German politics since the 1970s," Benedict said, represented a "cry for fresh air which must not be ignored or pushed aside." His comments prompted a burst of spontaneous applause, though he noted that he was not engaging in "propaganda" for any particular political party, leading to laughter on the floor.

On the plane ride from Rome to Berlin, Benedict addressed the sexual abuse of children by priests that threw the church in his native country into a deep crisis last year. "I can understand that some people have been scandalized by the crimes that have been revealed in recent times," he said, according to The Associated Press. Benedict said that there were both "good and bad fish in the Lord's net."

Chancellor Angela Merkel and President Christian Wulff met Benedict's Alitalia plane when it landed at Tegel Airport Thursday. Cannons fired a 21-gun salute to welcome the pontiff. Benedict, clad in white with a gold cross hanging on a chain, walked the red carpet on the tarmac.

The decision to allow Benedict to address the Parliament caused particular outrage among opponents who said it crossed the line between church and state. Dozens of members of the far-left Left Party boycotted the event. Hans-Christian Ströbele, a Green Party parliamentarian, stood up and left as the speech began.

Some of the boycotters joined protests in central Berlin's Potsdamer Plotz, organized by gay-rights and feminist groups that included demonstrators dressed as condoms and nuns and signs that read "Pope Go Home" and "I was sexually abused by the Church." German news agencies estimated the size of the crowd at about 20,000.Benedict was invited to make the address by Norbert Lammert, the president of the Bundestag. "Never before in history has a pope spoken before an elected German Parliament," Mr. Lammert said as he introduced the pope. "And seldom has a speech in this house created so much attention and interest before it was even given."

His predecessor, John Paul II, addressed the Italian parliament and several others, and last year Benedict spoke before the British political establishment in Westminster Hall, but Thursday's was the first time any pope had addressed the Bundestag.

Benedict acknowledged Germany's history of aggression in the 20th century, saying Germans "have seen how power became divorced from right, how power opposed right and crushed it, so that the State became an instrument for destroying right." He praised those who resisted the Nazi regime. Benedict grew up under Nazism. He came from an anti-Nazi family and was an unwilling member of the Hitler Youth.

Instead of a pleasant visit to his native land, the trip to Germany promised to be a journey to one of the front lines in the battle over the future of the Roman Catholic Church. The protests and demonstrations over the pope's visit are a far cry from the jubilation set off here by his election to the papacy more than six years ago. There was, many Germans say in hindsight, a naïveté to that celebration, which ignored the collision course between an increasingly secular society and a church leader set on a conservative, traditional path.

Reporting was contributed by Judy Dempsey and Victor Homola from Berlin and Rachel Donadio from Athens.