KRAKOW, Poland—World Youth Day, the massive gathering of Catholic youth from around the globe unfolding this week in Krakow, is a celebration of faith. Millions of young people are currently roaming the streets singing, praying and making new friends, and throughout the city, a spirit — and noise — of celebration is palpable.

Friday, however, was a reality check kind of day from the pope.

During a haunting Way of the Cross ceremony Friday night, against the backdrop of the brutal murder earlier in the week of a French priest by Islamic State-inspired assassins, Francis asked, ” Where is God, when innocent persons die as a result of violence, terrorism and war?”

Early in the morning, Pope Francis’ silent visit to the death camp of Auschwitz-Birkenau spoke volumes. The only actual words from the pontiff shared at that moment are ones he didn’t actually speak, but wrote in the visitor’s book: “Lord, have mercy on us. Lord, forgive so much cruelty.”

Early in the afternoon he visited a pediatric hospital in Krakow, where the suffering of the young patients clearly moved Francis, who’s made such visits during his trips abroad a standard part of his itinerary.

Later in the day, Francis once again met with the young pilgrims in Krakow, this time to lead them in the prayer of the Way of the Cross. In many ways, it’s the saddest prayer in Catholicism, formed by a fourteen-stations representation of Jesus’ death on the Cross.

According to Christian teaching, had it not been for that redeeming gesture, God’s greatest gift to humanity, the entire world today would be like Auschwitz-Birkenau, the Nazi concentration camp where an estimated 1.1 to 1.5 million people, most Jews, were killed during the Second World War.

Christianity teaches that without the cross, the world would be a place without mercy. And despite some stories of humanity during the Holocaust that throughout the years have emerged, the Nazis wanted for Auschwitz to be just that.

“By embracing the wood of the cross, Jesus embraced the nakedness, the hunger and thirst, the loneliness, pain and death of men and women of all times,” Francis said on Friday afternoon.

God, Francis told the hundreds of thousands gathered in Krakow’s Blonia Park, is found wherever there’s suffering.

“Where is God, if evil is present in our world, if there are men and women who are hungry and thirsty, homeless, exiles and refugees? Where is God, when cruel diseases break the bonds of life and affection? Or when children are exploited and demeaned, and they too suffer from grave illness? Where is God, amid the anguish of those who doubt and are troubled in spirit?” Francis asked.

Little imagination is needed to add “Where was God in Auschwitz?” or “Where is God in Prokocim Pediatric Hospital?”

“These are questions which, humanly speaking, have no answer,” the pope said.

“We can only look to Jesus and ask him. And Jesus’ answer is this: ‘God is in them’. Jesus is in them; he suffers in them and deeply identifies with each of them. He is so closely united to them as to form with them, as it were, ‘one body,’” he continued.

The Way of the Cross, Francis said, is a reminder of the importance of imitating Jesus through the fourteen works of mercy, seven corporal and seven spiritual, which the pontiff listed.

Through the corporal works of mercy, feeding the hungry, giving drink to the thirsty, clothing the naked, sheltering the homeless, visiting the sick and those in prison, and burying the dead, the pope told youth to “serve the crucified Jesus,” who’s present in the marginalized, the disadvantaged, the persecuted, refugees and migrants.

He then listed the spiritual works of mercy: Counseling the doubtful, instructing the ignorant, admonishing sinners, consoling the afflicted, pardoning offences, bearing wrongs patiently, praying for the living and the dead.

“In welcoming the outcast who suffer physically and welcoming sinners who suffer spiritually, our credibility as Christians is at stake,” Francis said.

On Thursday, during the opening ceremony of World Youth Day, a week-long event hosted every two or three years in different cities, Pope Francis appealed the youth not to opt for “early retirement” and not to let anyone tell them they can’t change what’s wrong in the world.

This Friday, the pontiff told them that Jesus wants to use them as a “concrete response to the needs and sufferings of humanity.”

“He wants you to be signs of his merciful love for our time! To enable you to carry out this mission, he shows you the way of personal commitment and self-sacrifice. It is the Way of the Cross,” Francis said.

The suffering Francis spoke about was represented in spades at the Via Crucis rite, as were those who today put the works of mercy into practice as part of their day-to-day lives. Each one of the 14 stations represented one of those works of mercy.

This way, the first one, “Jesus is sentenced to death” became welcoming the pilgrims-homeless. During the actual representation of the stations, members of the Community of Sant’Egidio, which is currently leading the Catholic Church’s response to the migrant crisis in Europe with a humanitarian corridor from the Middle East to Europe, carried the cross.

The third station, “Jesus falls for the first time,” stood for admonishing the sinners. At that point, young Iraqi pilgrims, who came to Krakow with the help of the papal charity Aid to the Church in Need, carried the cross.

The eleventh station, “Jesus is nailed to the Cross,” turned into an appeal to bear wrongs patiently, with the Missionary Sisters of Charity of Mother Teresa of Calcutta taking the stage. Mother Teresa is set to be declared a saint by Pope Francis on Sept. 4 in a massive Rome ceremony.

The reflections were written by Krakow’s Auxiliary Bishop Grzegorz Rys.

Along the way, each station was represented with different artistic forms, such as modern dance, mural painting, aerial acrobatics, computer animation and street art.