Pope Francis, deep into his 80s, slowed by illness and aware that his window for bringing lasting change to the Roman Catholic Church is closing, arrived in Portugal on Wednesday for a weeklong meeting of the world’s young Catholics, in whose hands will rest the ultimate success of his vision for a more pastoral and inclusive faith.

“In Lisbon, I would like to see a seed for the world’s future,” Francis, 86, said in video remarks to young people ahead of World Youth Day, which he first attended in Brazil at the start of his papacy 10 years ago. The church, he warned, could not be a “club” for the elderly. “If it becomes something for old people, it will die.”

The five-day tour to Portugal is the pope’s 42nd overseas trip, and is expected to attract about a million people from more than 200 countries, many of them between the ages of 16 and 35, and many in sync with Francis’ emphasis on inequality and climate issues. Participants will even be able to track their carbon footprint on an event app.

The meeting will also be attended by more than 700 bishops and 20 cardinals, and comes as Portugal grapples with an exploding clerical sex abuse crisis. Francis is also preparing for a major meeting of the world’s bishops — and for the first time women and laypeople — to tackle divisive issues like the role of women and L.G.B.T.Q. Catholics in the church.

Throughout his papacy, Francis has sought to draw more people into the church by making it more welcoming and close to its people, and less focused on rules and abstractions, power and rank. The World Youth Day, and Francis’ emphasis on the young, is a way to keep a lifeline open to the future as the church’s present, especially in the developed world, has been marked by scandals, decreasing numbers and declining cultural relevance.

It is instead in the developing world, especially Africa and Asia, where young Catholics are more fervent. But those are also places where the church is more conservative.

Francis has steadily filled his hierarchy with prelates in his image, but has also often balked before opportunities to make concrete changes to church policy, such as allowing married men to become priests in remote areas where the faithful cannot receive communion and other sacraments.

His supporters argue that the death of the retired and deeply conservative Pope Benedict XVI last year freed Francis from an awkward brake. And they say that his own health problems — he recently left the hospital after yet another surgery — have added urgency for him to start walking in a new direction, rather than just talk about it.

There is also a view that Francis may be content to prepare the ground for a major shift, and to let his successor take the real leaps. But it is not clear who will follow Francis as pope, even as he packs the College of Cardinals that will elect his successor.

In the meantime, Francis is also taking steps to rejuvenate the church. In a geriatric institution, he has put middle-aged men who share his pastoral approach to leadership in charge of major archdioceses like Buenos Aires, Brussels and Madrid. He has appointed cardinals in their 50s — spring chickens for the church — who will in theory vote to select popes in the conclaves for decades to come.

The prelate in charge of World Youth Day, Americo Aguiar, only 49, will become a cardinal at a Sept. 30 ceremony during which Francis will elevate 21 churchmen, adding to the percentage of voters he has created ahead of the next conclave, which will pick his successor once he dies or retires. Bishop Aguiar will be the second-youngest cardinal after the head of the church in Mongolia, where Francis will travel at the end of August.

Another relatively young new cardinal will be Manuel Fernández of Argentina, 61, who was recently made the powerful head of the office of church orthodoxy. His own youthful poetry about kissing has led to mockery and disdain from the church conservatives Francis is seeking to thin out.

Pope John Paul II started World Youth Day in 1986, to demonstrate that the church had a younger, fresher face. The Lisbon event will be the 16th such engagement; it was initially scheduled for last year but was postponed because of the coronavirus pandemic.

But far from grass-roots movements, the events are rigorously planned by the church establishment and have not translated into an organic return back into the pews. Within the church, many often consider them glorified hookup events, a view the hierarchy has sought to tamp down on.

“They do not need neither joints, nor condoms, nor alcohol to live an unforgettable joy,” the bishop of Cordoba, Demetrio Fernandez, said in a recent weekly letter.

The Portuguese church has also sought to portray the event as interreligious, and not strictly Catholic, with the participation of Protestants, Muslims and Jews. It was an “event open to all,” Cardinal Manuel Clemente, patriarch of Lisbon, told reporters last month.

“Certainly there will be a strong Catholic presence,” he added.

That presence is shrinking though, even in once-devout Portugal. The Portuguese Catholic church, like so many across Europe, has consistently diminished and weakened, even as evangelicals, many of them Brazilian, have multiplied their numbers.

Lisbon, once a pious capital, is now a cosmopolitan and increasingly secular city, and newly revealed sexual abuse scandals in the Portuguese church seem destined to accelerate its falling numbers — and to alienate the youth Francis hopes to inspire.

In February, a live broadcast of experts appointed by Portugal’s own church leaders reported that at least 4,815 boys and girls, most between 10 and 14 years old, were abused since 1950. The experts read accounts of some victims in front of the country’s top bishops, and the commission’s leader said that more than 100 priests suspected of abuse still had active church roles at the time of the report’s publication.

Bishop Aguiar has said Francis will meet with some of those victims during his visit, even as the Portuguese church has waffled on possible reparation payments. Francis is expected to address the issue during his visit.

The distance between the country and the church has also been shown by the criticism for the tens of millions of euros directed to finance the event. In the days before the event, a Portuguese artist, Bordalo II, laid out a red carpet made from oversized 500-euro bank notes.

“In a secular state,” the artist wrote, “at a time when many are struggling to keep their homes, their jobs and their dignity, millions of public money are going to sponsor the tour of the Italian multinational.”

That is not the message the Vatican is hoping for.

Instead, Francis will seek to animate young crowds with talk of peace on a continent once again marked by war. Francis himself has made fruitless, and critics say counterproductive, efforts to broker peace in Ukraine that Ukrainians have worried play into Russian hands.

After a halting start, Francis has more clearly put the fault of the war on Russian aggression.

The pope is likely to stress his calls for peace on Saturday, when he is scheduled to return to the Shrine of Fatima, a pilgrimage site north of Lisbon where tradition holds that the Virgin Mary appeared to three shepherd children in 1917. She delivered a prophecy that the world would be destroyed if it did not convert, and that the pope could stay God’s angry hand if he brought atheists and Communist Russia to her “immaculate heart.”

Last year, Francis consecrated all the world, but especially Russia and Ukraine, to the Immaculate Heart of Mary before a statue of Our Lady of Fatima in St. Peter’s Basilica.