Pope Benedict held the final Mass of his 4-day visit to Spain Sunday, urging some 1.5 million young people at the Roman Catholic Church's youth festival to become active in their church and avoid trying to find faith on their own.

Benedict told pilgrims from 193 nations to spread their faith even if they are met with rejection or indifference.

The open-air Mass, conducted in Spanish, was attended by Spain's King Juan Carlos and Queen Sofia.

After his remarks, the pope designated Rio De Janeiro in Brazil as the next site of the World Youth Day festival in 2013.

Benedict held a prayer vigil Saturday evening at the Cuatro Vientos airport near Madrid, but a huge thunderstorm forced the pontiff to cut short his speech. He thanked the gatherers for their “joy and endurance,” adding that their strength was “greater than the rain.”

Earlier in the day, firefighters had sprayed the crowds with water from hoses in a bid to stave off the near 40-degree heat.

This was the pontiff's third World Youth Day – a gathering of young Catholics from around the world. The first such event was launched a quarter century ago by Pope John Paul II in a bid to reinvigorate and spread the faith among the young.