KRAKOW, Poland – Popes pay tribute to their predecessors all the time in small ways – with footnotes to their documents, for instance, or references to their teaching, or simply by mentioning them in various contexts.

If ever an entire papal morning had “homage” written all over it, however, it was Pope Francis’ visit on Saturday to the Sanctuary of Divine Mercy, in the Krakow neighborhood of Lagiewniki, and then his Mass for priests and religious at the Sanctuary of St. John Paul II.

Divine Mercy, of course, is the devotion associated with St. Faustina Kowalska, a Polish nun who entered the Congregation of Sisters of Our Lady of Mercy in 1925 and later reported that she soon began to have visions of Jesus, Mary and several saints. During one of these visions, she recounted, she was instructed to commission a painting of Jesus based on Divine Mercy, with rays of red and white light coming out from his heart and the signature line, “Jesus, I trust in You.”

It was Krakow’s Archbishop Karol Wojtyła, later Pope John Paul II, who in 1965 began a beatification process for Kowalska, and who promoted the Divine Mercy devotion aggressively. In fact, the reason the site is called a “shrine” is because Wojtyla designated it as such, and in 1985 he declared that Lagiewniki as the “capital of the Divine Mercy devotion.”

In 1997, John Paul II came back as pope to pray at the tomb of St. Faustina. When Benedict XVI made his own visit he unveiled a statue of John Paul II – if you’re counting, the seventh statue of John Paul in the city of Krakow.

In 2000, John Paul II declared Kowalska the first saint of the new millennium, and decreed that the first Sunday after Easter would be observed as “Divine Mercy Sunday” – another request that Kowalska had said came from her visions.

So great was John Paul’s attachment to the Divine Mercy devotion that many observers believe he stubbornly clung to life for a few extra days in April 2005 so that he could die on the feast’s vigil. From there, it seemed natural that John Paul would be beatified on Divine Mercy Sunday in 2011, and canonized along with Pope John XXIII on Divine Mercy Sunday in 2014.

In other words, there are few spots on earth more tied to John Paul II than Lagiewniki, and simply by setting foot in the sanctuary, Francis was thus bearing witness to John Paul II’s memory.

As Francis arrived in the convent church (a few minutes early, as he has throughout the trip), 150 members of the of Sisters of Our Lady of Mercy greeted him with up-beat Spanish singing and waving flags with the image of World Youth Day on one side and St. Faustina on the other. He prayed in front of a statue of Faustina with her famous diary, then led the nuns in reciting the “Hail Mary” and delivered a short blessing.

He signed the guest book by citing, in Spanish, a line from the Gospel of Matthew (which is itself a citation from the Book of Hosea): “It is mercy I desire and not sacrifices.”

Francis then moved on to the larger, modern structure at the Lagiewniki shrine, walking out onto a balcony to greet the enthusiastic crowd, greeting them in Spanish with a brief fervorino about mercy and leading them in a short prayer.

Francis then walked through the Holy Door at the sanctuary in keeping with his own Year of Mercy, a jubilee inspired in part by Faustina and John Paul II. Afterwards, he heard the confessions of five young people, in Spanish, Italian and French. Later, he also spontaneously agreed to hear the confession of a priest who asked him for it while greeting him.

Then, Francis put an exclamation point on the John Paul II tribute by saying Mass in a sanctuary expressly dedicated to his memory, founded in June 1995 on the strength of a decree by Cardinal Franciszek Macharski, who was John Paul’s successor as the Archbishop of Krakow, and whose expansion was overseen by Cardinal Stanislaw Dziwisz, who served John Paul as his priest-secretary and right-hand man.

The entire complex called the “Have No Fear!” Center, in tribute to John Paul’s most famous exhortation, which captures in three short words the entire spirit of his almost 27-year papacy. It contains a volunteer center, an academic institute, and a number of churches and chapels.

Francis cited another famous line associated with John Paul in his homily at the Mass: “How can we fail to hear its echo in the great appeal of Saint John Paul II: ‘Open the doors’?”

The pontiff largely devoted his homily to a characteristic plea to priests and religious not to become closed in on themselves, but to get out into the street to meet the needs of the world.

“Jesus directs us to a one-way street: that of going forth from ourselves,” the pope said. “It is a one-way trip, with no return ticket. It involves making an exodus from ourselves, losing our lives for his sake.”

The pope called his audience to mission, rooted in the virtue of mercy.

“There is room left for the signs needing to be worked by us, who have received the Spirit of love and are called to spread mercy,” the pope said.

“It might be said that the Gospel, the living book of God’s mercy that must be continually read and reread, still has many blank pages left. It remains an open book that we are called to write in the same style, by the works of mercy we practice.”

Throughout the morning, Francis did not explicitly refer much to either St. Faustina or St. John Paul II, but in effect he didn’t have to. The entire experience indicated just how much the legacy of both great Polish saints hangs over the Year of Mercy, and, for that matter, the kind of Catholic Church Francis is trying to lead.