Pope Benedict XVI addressed Germany's parliament in the historic Reichstag building Thursday, warning that politicians must not sacrifice ethics for power and evoking the Nazi excesses of his homeland as a lesson in history.
Amid scattered protests outside and a boycott by some lawmakers, Benedict began his first state visit to Germany in a bid to stem the tide of Catholics leaving the church while acknowledging the damage caused by the clerical sex abuse scandal.
The pope spoke for 20 minutes in the Reichstag, which was torched in 1933 in an incident used by Hitler to strengthen his grip on power.
"We Germans know from our own experience" what happens when power is corrupted, Benedict said, describing Nazis as a "highly organized band of robbers, capable of threatening the whole world and driving it to the edge of the abyss."
But he said even under the Nazi dictatorship resistance movements stuck to their beliefs at a great risk, "thereby doing a great service to justice and to humanity as a whole."
He also urged all Germans not to ignore religion.
"Even today, there is ultimately nothing else we could wish for but a listening heart _ the capacity to discern between good and evil, and thus to establish true law, to serve justice and peace," he said.
Benedict also voiced strong support for Germany's ecological movement, calling it "a cry for fresh air which must not be ignored or pushed aside."
After the speech, he met with a 15-member Jewish delegation, noting that it was in Berlin that the annihilation of European Jews was organized.
"The supposedly `almighty' Adolf Hitler was a pagan idol, who wanted to take the place of the biblical God," Benedict said according to a prepared text.
The Bavarian-born pontiff was met on a red carpet at Berlin's Tegel airport by German Chancellor Angela Merkel and President Christian Wulff at the start of his four-day visit. He greeted members of the German Catholic Church, and accepted a bouquet from children waiting with small yellow-and-white Vatican flags.
About 20 protesters stood outside the airport, holding banners with slogans like "Against anti-Semitism, sexism and homophobia" and "My body, my choice."
The Vatican's views on contraception, the role of women, homosexuality and its handling of the sexual abuse scandal that rocked Germany last year are seen by many in Germany as outdated.
About 100 lawmakers from opposition parties boycotted the pope's appearance, claiming it violated the church-state separation. But Benedict looked out on a mostly full house as guests occupied the empty seats and finished his speech to a standing ovation.
Police estimated only "several thousand" protesters showed up at the capital's Potsdamer Platz, far fewer than organizers had predicted. Some 6,000 officers were on duty throughout the city. In a rally during the pope's speech, protesters held signs with slogans like "Not welcome."
"Today is a good day to be visible," Maria Pflugradt, a 22-year-old student from Cottbus told The Associated Press. "Not only because he is against homosexuals, but also because the church has made far too many mistakes in the last centuries."
In parliament, Speaker Norbert Lammert welcomed the pope, noting that the last time there was a pontiff of German origin Germany didn't yet even exist as a state.
"Germany is a country that over centuries was strongly marked by religion and religious wars," Lammert said. "A country whose Christian traditions of belief also influence the constitution we have today."
But flagging Christian influence in Europe was one of Benedict's key themes.
"We are witnessing a growing indifference to religion in society," he said at a formal welcoming ceremony at the German president's Bellevue palace. He called religion a foundation for a successful society and said its values were essential for freedom.
Benedict said the presidential palace, which was destroyed in World War II, was a reminder of German history.
"A clear look at the past, even at its dark pages, enables us to learn from it and to receive an impetus for the present," the pope said.
Over the next four days, the pope has meetings with leaders of Germany's Jewish and Muslim communities, three Masses and an ecumenical service with Lutheran church members.
More than 250,000 people are registered attend his Masses, starting with an open-air service Thursday night in Berlin's Olympic Stadium, built by the Nazis for the 1936 games. Some 70,000 enthusiastically cheered the pope as he drove through the stadium in his popemobile, greeting the faithful and kissing several babies.
"Looking into the wide expanse of the Olympic Stadium, which you are crowding in such a great number, fills me with great joy and confidence," he said.
Benedict urged the crowd not to view the church merely "as one of many organizations within a democratic society," but as the source of their salvation.
The faithful appeared moved as they left after the service in German and Latin.
"It was beautiful. The service surpassed all my expectations," said Heidi Frank, 49, who had traveled 310 miles (500 kilometers) from the southern German city of Regensburg to see the pope. "The atmosphere was impressive _ the entire community praying, you don't get that every day," said Jaqueline Hoehns, 21, from Berlin.
During his trip, Benedict was not expected to meet with Roman Catholic dissidents who have called for allowing women priests and ending mandatory celibacy for priests.
He told reporters on the plane the church needs to examine why people have been leaving recently and the part that the cleric abuse scandals have played in that.
"I can understand that some people have been scandalized by the crimes that have been revealed in recent times," he said. "(There are both) good and bad fish in the Lord's net."
The German president, himself Catholic, warmly welcomed the pope and praised the role played by the Church in supporting German reunification more than 20 years ago. But Wulff also expressed his understanding of why many Germans can no longer relate to the church.
"It is important for the Church to remain close to the people and not to turn inward on itself," Wulff said, noting that as a remarried divorcee, he is not allowed to accept communion. "Many ask themselves how mercifully it treats people who have suffered breakups."
Vatican spokesman the Rev. Federico Lombardi called the president's remarks "beautiful and very sincere."
Geir Moulson, Melissa Eddy, David Rising and Juergen Baetz contributed to this report.