Even for jaded journalists World Youth Day came as a surprise. The organisation was appalling. Public transport collapsed. The ATMs ran out of money. The field where the young people were supposed to sleep overnight and attend Mass on Sunday turned into a quagmire after heavy rain. Even the mayor of Rio de Janeiro admitted that the city had scored "closer to zero than ten".
The three million young people who gathered on Rio's famous Copacabana beach were wet, crowded, sleepless, and standing in queues for foetid portable toilets.
But there were few complaints. Instead, the atmosphere was upbeat and cheerful. The Pope, the new Pope, the first Latin American Pope, was there. It was a time of joy.
"After more than 25 years of covering wars, drug trafficking, riots, protests, coup d'états and, yes, five Papal tours in Latin America, I have to admit that I am not very easy to impress," wrote Lucia Newman, Al Jazeera's Latin American editor. "But without hesitation, I confess that the scene on Copacabana Beach on Saturday night and the early hours of Sunday was extraordinary."
Sometimes the media misses a story which is right under their noses. If the Pope can draw three million young people from all over the world to an event like this, is Christianity really in its twilight years? Will the next generation really be godless and secular?
Apart from promoting piety and enthusiasm World Youth Day helps to give Catholic teachings, however counter-cultural, a firmer intellectual foundation. Many of them are going to apply these lessons to their home life - and their politics - in the years to come.
For example, at least two million of the pilgrims received an easy-to-read manual on bioethics covering issues like IVF, abortion, and organ transplants. This will surely help some of them draw lines in the sand when they confront issues back home later in life.
It is also sure to spark greater commitment to evangelism. This was the core of the message of Pope Francis. Over and over again he insisted that his listeners had to share their faith with their friends:
"The experience of this encounter must not remain locked up in your life or in the small group of your parish, your movement, or your community. That would be like withholding oxygen from a flame that was burning strongly. Faith is a flame that grows stronger the more it is shared and passed on… Jesus did not say: 'if you would like to, if you have the time', but: 'Go and make disciples of all nations'."
Clearly what Francis has in mind is not just spraying peach blossom air freshener in musty cathedrals. He is flinging windows open and energetically engaging the secular world. He used sporting images to exhort the youth to evangelise:
"Young people, please: don't put yourselves at the tail end of history. Be active members! Go on the offensive! Play down the field, build a better world, a world of brothers and sisters, a world of justice, of love, of peace, of fraternity, of solidarity. Play always on the offensive!"
He also played the role of tough-love coach for his lieutenants, the Catholic bishops, encouraging them to do less deskwork and more footwork: "We cannot keep ourselves shut up in parishes, in our communities, in our parish or diocesan institutions, when so many people are waiting for the Gospel!"
For many of the bishops, feeling glum at bad news about scandals and declining church attendance, this must have been a George Patton moment when the supreme commander whips his troops into shape. The message was: no moaning, no whingeing. You have a "revolutionary" faith. Use it!
"You know that in the life of a Bishop there are many problems that need to be resolved. And with these problems and difficulties, a Bishop's faith can grow sad. How horrible is a sad Bishop! How bad is that!"
The stunning success of Rio is a pointer to the future.
For the last 50 years, the Catholic Church, which provides most of the firepower for Western defenders of traditional values and human dignity, has been slowly cleaning up after a tsunami of 20th century secularisation. At first progress was all but imperceptible. In the 60s and 70s many lay people stopped going to church and waves of priests defected. The effects of this era still reverberate.
But from the late 70s, the Church recovered its vitality in three stages. In the first, John Paul II gave it fresh discipline, confidence and relevance. Using his immense charm and prestige, he reaffirmed traditional teaching without making it seem old-fashioned. And after the fall of Communism, the Catholic Church was clearly the world's staunchest defender of human dignity.
In the second, Benedict XVI emerged as the world's leading public intellectual. It became obvious that the most powerful critique of moral and cultural relativism and a resurgent Islam was to be found in the Church.
With Francis, a third stage has arrived: energetic and unashamed evangelism. This was an important theme for his predecessors, too, but for Francis it is nearly the only one. In every single speech, homily and document there thunders the drumbeat of evangelism.
And if you want to know whether the message is reaching people, just look at the statistics. In 2006 the Rolling Stones also featured at Copacabana Beach. About 1.5 million people flocked to what has been described at the world's biggest ever free rock concert. Three million came to Pope Francis's gig - and he is seven years older than Mick Jagger.
What World Youth Day at Rio showed is that Christianity is far from being ready for the dustbin of history. Instead, it's on the ultimate revival tour.