CZESTOCHOWA, Poland (AP) — Pope Francis, visiting a shrine cherished by Poles, praised native son St. John Paul II on Thursday as a “meek and powerful” herald of mercy, and honored the countless “ordinary yet remarkable people” in Poland who held firm to their Catholic faith throughout adversity in the former Communist nation.

The Argentine pontiff, who had never had set foot in Eastern Europe before this week’s five-day pilgrimage to Poland, gazed in awe for several minutes as he studied the Jasna Gora monastery shrine’s iconic image of the so-called Black Madonna. The faces of Mary and Baby Jesus in the icon are blackened by centuries of varnish and candle soot since the artwork became the object of veneration starting in the 14th century.

A silver screen was raised slowly and dramatically to unveil the image as Francis stood silently in admiration and then prayed.

Then, during an outdoor Mass in the southern city of Czestochowa, before a crowd that appeared to number more than 100,000, Francis lavished praise on Poland’s steadfast Catholic legacy as he urged Poles to hold fast to their faith.

As Francis walked up to the altar he tripped and fell over, but was quickly helped to his feet by others. He went on to deliver a long sermon and a Vatican spokesman, Greg Burke, later said “the pope is fine.”

Czestochowa Archbishop Waclaw Depo said Francis fell because he had closed his eyes and appeared to miss a step. “He did not even complain at all. He never said a word,” Depo added.

The Mass was held in celebration of the 1,050th anniversary this year of the Poland’s acceptance of Roman Catholicism. The baptism of a medieval king in 966 put Poland on course to be part of the Latin-speaking Western world, setting it apart culturally from Orthodox nations in the region. Polish President Andrzej Duda and other political leaders were among those attending the Mass.

“Our minds turn to so many sons and daughters of your own people, like the martyrs who made the defenseless power of the Gospel shine forth, like those ordinary yet remarkable people who bore witness to the Lord’s love amid great trials,” Francis said in his homily, speaking in Italian and pausing for a priest to translate his words into Polish.

He then cited two beloved Polish saints, praising those “meek and powerful heralds of mercy who were Sts. John Paul II and Faustina. Through these channels of his love, the Lord has granted priceless gifts to the whole Church and to all mankind.”

Francis then recalled the far less famous soldiers of the faith in Poland.

“Your own history, shaped by the Gospel, the cross and fidelity to the church, has seen the contagious power of a genuine faith, passed down from family to family, from fathers to sons and above all from mothers and grandmothers, whom we need so much to thank,” he said.

Francis urged today’s Poles to stay united even as their nation is divided over the issue of refugees and migrants, especially those who aren’t Christians. He prayed that Poles would have “the desire to leave behind all past wrongs and wounds, and to build fellowship for all, without ever yielding to the temptation to withdraw or to domineer.”

A right-wing government came to power in Poland last year that has faced international scrutiny for eroding past democratic gains, and critics say they have seen a rise in xenophobic sentiment.

Worry about bad weather prompted a last-minute change the pope’s travel plans, with Francis opting to take a car instead of a military helicopter to Czestochowa, 100 kilometers (60 miles) from Krakow. The gray skies held into the Mass but he was able to return to Krakow by helicopter.

Francis’ visit to Poland centers around a Catholic youth jamboree that has drawn hundreds of thousands of participants this week. He will have his first big meeting with the young faithful in a Krakow meadow on Thursday evening.

Earlier in the day, Francis made an unscheduled stop at a clinic to visit and pray for comatose Cardinal Franciszek Macharski, an-89-year-old retired prelate who had been archbishop of Krakow.

In his first speech after arriving Wednesday, Francis called on Poles to be compassionate and welcoming to those in need, especially refugees. He also met with Duda, whose populist government has virtually slammed the door on asylum-seekers and migrants from the Middle East and Africa seeking the safety and economic promise of Europe.

Monika Scislowska in Krakow and Vanessa Gera in Warsaw contributed to this report.