Pope Benedict has urged hundreds of thousands of young people to avoid a "spiritual desert" that was spreading across the world.  The pontiff delivered his message Sunday at the Catholic Church's World Youth Day in Sydney, Australia.  From Sydney, Phil Mercer reports.

Pope Benedict presided over Mass at a spectacular finale to the Catholic Church's six-day-long youth festival in Sydney.

He told worshippers at a city race course that had been transformed for the event that the world needed "renewal," and he challenged the young pilgrims to be agents of change.

The pontiff flew by helicopter over legions of pilgrims, many of whom had camped out in cold weather in preparation for Sunday's events.

On Saturday, the pope apologized for the "evil" and "shameful" sexual abuse of children by pedophile clergy.  His contrition did not satisfy victims and their families, which accused the Catholic church of attempting to cover up the true extent of the problem.

The pontiff's views on birth control and homosexuality have also been challenged during World Youth Day by the NoToPope Coalition, a grouping of atheists, gays and left-wing students.

A chief aim of the international festival was to guide young Catholics through life's complex maze. The pope urged restraint at a time of 'insatiable' consumerism and criticized television and the internet for promoting sexual exploitation as entertainment and of glorifying violence.

The Vatican will undoubtedly see the event as a success, given the enthusiasm shown by the young pilgrims.

"People wait their whole lives to see the Pope and it's something that we got to do when we were 19 with our best friends and with people from around the world, so it's something that we're never going to forget," an American teenager said.

"I don't have words to explain how I happy I feel," said a Mexican teenager.  "To be here is very, very important for me because I confirm my faith in God, in [the] Church and meet a lot of people who came to Australia."

"It has been confirmed to me that it is the one faith.  All the questions I've asked have been answered and it's the truth," a Kenyan pilgrim said.  "It's the whole truth."

There is some concern among Church officials that fewer people are heeding this spiritual message. The pope has admitted that the Catholic Church was in "crisis" in Western countries because many had lost faith in God.

World Youth Day has been held every two or three years since 1986.

At the close of his address, the Pope announced that the next World Youth Day, in 2011, would be held in Spain and promised pilgrims that he would attend.