Young Catholics at World Youth Day in Sydney have been urged to struggle against their "fat, relentless egos" and commit to their faith.
Sydney Archbishop George Pell made the call after 140,000 pilgrims chanted, sang and danced their way to Barangarooo, near Sydney's Darling Harbour, for today's World Youth Day (WYD) opening mass - the largest celebrated in Australia.
Addressing the colourful crowd at the opening of six days of celebrations, Cardinal Pell said following Christ required struggle, sacrifice and self discipline.
"Following Christ is not cost free, not always easy, because it requires struggling against what St Paul called `the flesh', old fat relentless egos, old fashioned selfishness," he said in his homily.
"It is always a battle, even for old people like me.
"Don't spend your life sitting on the fence, keeping your options open, because only commitments bring fulfilment."
Dr Pell told the faithful, including 26 cardinals, 400 bishops and up to 4,000 priests, that many people had found their life's calling at WYD events.
His address was preceded by a welcome from Prime Minister Kevin Rudd, who was clapped and cheered as he addressed the pilgrims in several languages.
"Australia welcomes the youth of the world to Sydney, Australia welcomes the youth of the world to this celebration of faith and this celebration of life," Mr Rudd said.
With chants of "Aussie, Aussie Aussie, Oi, Oi, Oi" in the background, Mr Rudd said it was a time to speak about all that was right in Christianity and the church.
"It was the church that began first schools for the poor, it was the church that began first hospitals for the poor, it was the church that began first refuges for the poor, and these great traditions continue for the future," he said.
"Christianity has been an overwhelming force for good in the world."
Mr Rudd said Australia had a proud Christian heritage, and he hoped pilgrims would be enriched by their time here.
Earlier, indigenous Australians took centre stage in the pre-mass celebration, dancing, singing and playing didgeridoo for the joyful crowd.
They followed a parade of flags and the arrival of the WYD cross and a large religious icon depicting Madonna and child, both of which have travelled around Australia for the past 12 months.
Dr Pell said he expected pilgrims would be uplifted over the course of the six-day Catholic youth event, which ends on Sunday with mass celebrated by Pope Benedict XVI.
However, he urged them to make time for quiet reflection.
"During this week we have every right to rejoice and celebrate the liberation of our repentance, rejuvenation of our faith," he said.
"And the young ones, I give a gentle reminder that in your enthusiasm and excitement, you do not forget to listen and pray."
