St John Paul II's former secretary urged young Catholics to share their faith, experiences and hopes and spread a "message of divine mercy" worldwide during World Youth Day.

"We come from every nation under heaven, like those who came in great numbers to Jerusalem on Pentecost Day, but there are incomparably more of us now than 2,000 years ago, because we are accompanied by centuries of preaching the Gospel," Kraków Cardinal Stanislaw Dziwisz said during the July 26 opening Mass.

"We bring experience of various cultures, traditions and languages. But what we also bring are testimonies of faith and holiness of our brothers and sisters, followers of the risen Lord, of past generations as well as the current generation," he said.