Pope Benedict XVI celebrates Mass at Yankee Stadium in New York. The Mass was the final public event in Benedict's U.S. tour.

New York ? Pope Benedict XVI celebrated Mass and American Catholicism in storied Yankee Stadium on Sunday, telling his massive U.S. flock to use its freedoms wisely as he closed out his first papal trip to the United States.

Benedict beamed before a joyous crowd of 57,000, hours after making a solemn stop to pray at the site of the Sept. 11, 2001, terrorist attacks on the World Trade Center.

He called the Mass “a summons to move forward with firm resolve to use wisely the blessings of freedom, in order to build a future of hope for coming generations.”

And he repeated a core message of his six-day pilgrimage – that faith must play a role in public life, citing the need to oppose abortion.

The unwavering truth of the Roman Catholic message, he said, guarantees respect for the dignity of all, “including the most defenseless of all human beings, the unborn child in the mother’s womb.” The crowd applauded the line.

Outside the stadium, two dump trucks filled with sand blockaded 161st Street before Mass, an extra level of security along with the heavy police presence. Pilgrims without tickets pushed up against metal police barricades, hoping to get a glimpse of the arriving pope.

Inside, ad-splashed outfield walls were draped in white with purple and yellow bunting. A white altar perched over second base, and the papal seal covered the pitcher’s mound, suspended by white and yellow ribbons.

“I have never seen Yankee Stadium so beautiful, and I have season’s tickets,” said Philip Giordano, 49, a tax attorney from Greenwich, Conn., who won seats in the loge section behind home plate through a parish lottery.

Added his wife, Suzanne: “I’m hoping to feel something from (Benedict). Everyone who has seen him says they crumple, their knees buckle. You come away just feeling different.”

New Orleans crooner Harry Connick Jr., on the pre-Mass concert program, remarked that he is often asked if he’s a practicing Catholic. “Practicing?” he said. “I’m playing for the pope today.”

Benedict seemed to enjoy his long journey to the altar in the popemobile, waving to people in the stands. From the altar, he stood to acknowledge the crowd’s roar when New York Cardinal Edward Egan welcomed him.

He praised the U.S. church, which has 65 million members, in his homily, saying that “in this land of freedom and opportunity, the church has united a widely diverse flock” and contributed greatly to American society.

The pope departed on a special airliner nicknamed “Shepherd One” after a farewell ceremony hosted by Vice President Dick Cheney, with Democratic presidential hopeful Hillary Rodham Clinton and President Clinton in attendance. “May God bless America!” he said before departing.

Earlier, on a chilly, gray morning, the pope blessed the site of the terrorist attacks and pleaded with God to bring “peace to our violent world.”

Addressing a group that included survivors, clergy and public officials, he acknowledged the many faiths of the victims at the “scene of incredible violence and pain.”

The pope also prayed for “those who suffered death, injury and loss” in the attacks at the Pentagon and in the crash of United Airlines Flight 93 in Shanksville, Pa. More than 2,900 people were killed in the four crashes of the airliners hijacked by al-Qaida.