NEW YORK (CNN) -- Pope Benedict XVI on Saturday recalled growing up during the Nazi era in his native Germany and stressed the "fundamental importance of freedom" as he addressed a rally of young people in New York.

Pope Benedict XVI greets the audience at a rally at St. Joseph's Seminary in Yonkers, New York, on Saturday. more photos »

"My own years as a teenager were marred by a sinister regime that thought it had all the answers," he told the crowd at St. Joseph's Seminary in Yonkers.

"Its influence grew, infiltrating schools and civic bodies as well as politics and even religion before it was fully recognized for the monster it was," the pope said.

"Many of your grandparents and great-grandparents will have recounted the horror of the destruction that ensued. Indeed, some of them came to America precisely to escape such terror."

As he praised the spread of democracy and respect for human rights, the pope cautioned about the dangers people face in the modern world.

"I am thinking of those affected by drug and substance abuse, homelessness and poverty, racism, violence and degradation -- especially of girls and women," the pope said.

And he decried "new injustices," including environmental problems.

The Earth "groans under the weight of consumerist greed and irresponsible exploitation," he said.

The pope received a rousing welcome at the rally, with about 25,000 young Catholics from throughout the United States cheering, chanting "We love you" and waving white and yellow scarves as he arrived. The crowd also sang "Happy Birthday" in German, applauding when the pontiff said he gave them an "A-plus" for their German pronunciation. Benedict turned 81 on Wednesday.

Before Saturday's rally, he blessed a group of children with disabilities and told them it was a special joy to spend time with them.

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"Sometimes, it is challenging to find a reason for what appears only as a difficulty to be overcome or even pain to be endured," the pope told the children and their caregivers.

"God has blessed you with life and with differing talents and gifts. Through these, you are able to serve him and society in various ways."

He shook hands with and touched the faces of the children, many of whom were in wheelchairs.

Earlier, Pope Benedict XVI again addressed the Catholic Church's sexual abuse scandal, assuring priests, nuns and other religious of his "spiritual closeness" as they recover from the scandal's damage.

"I have already had occasion to speak of this and of the resulting damage to the community of the faithful," he said during Mass at St. Patrick's Cathedral in New York.

"I join you in praying that this will be a time of purification for each and every particular church and religious community and a time for healing. I also encourage you to cooperate with your bishops who continue to work effectively to resolve this issue."

At a prayer service with U.S. bishops Wednesday in Washington, Benedict said the sexual abuse of children by priests has caused a "deep shame" and called it "gravely immoral behavior."

A day later, Benedict spoke and prayed with a small group of people who say they were sexually abused by members of the clergy.

Saturday's Mass for members of the religious community marked the third anniversary of Benedict's election to the papacy.

The pope entered the sanctuary in a grand procession, wearing gold-trimmed white vestments and a white papal miter embroidered with a gold cross.

The congregation greeted him with prolonged, enthusiastic applause after he was welcomed by Cardinal Edward Egan, archbishop of New York. Watch the pope celebrate Mass at St. Patrick's »

St. Patrick's, on Fifth Avenue, has been considered the center of Catholic life in the United States. It draws millions of visitors each year.

"I am particularly happy that we have gathered in St. Patrick's Cathedral," the pope told the thousands assembled beneath its vaulted roof.

"Perhaps more than any other church in the United States, this place is known and loved as 'a house of prayer for all peoples,' " he said, alluding to a verse from the Bible.

Earlier in the Mass, Mayor Michael Bloomberg addressed the clergy.

"Since its beginning, New York has stood as a beacon of religious tolerance and celebration," he said.

On Friday, Benedict visited Park East Synagogue, becoming the first pope to visit a Jewish house of worship in the United States.

"I find it moving to recall that Jesus, as a young boy, heard the words of Scripture and prayed in a place such as this," the pope said.

Congregation members presented the pope with a Passover Seder plate, placed at the center of the dinner table during the holiday marking the occasion when Jews were led out of slavery in Egypt. He was also given a box of matzo and a Haggadah, the prayer book used during Passover.

In turn, the pope presented Rabbi Arthur Schneier, leader of the Park East Synagogue, with a Jewish manuscript.

In his welcoming remarks, Schneier called the visit historic.

Benedict's three-day visit to New York is the second leg of the pope's six-day trip to the United States, his first since he was elected to the papacy.

On Sunday, the last day of his trip, he will visit Ground Zero and celebrate Mass at Yankee Stadium. E-mail to a friend

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