Pope Francis is presiding Friday over a special prayer for Ukraine that harks back to a century-old apocalyptic prophesy about peace and Russia that was sparked by purported visions of the Virgin Mary to three peasant children in Fatima, Portugal, in 1917.

Francis has invited bishops, priests and ordinary faithful around the world to join him in the consecration prayer Friday afternoon. And to hammer home its universal nature, the Vatican has translated the text of the prayer into three dozen languages. Retired Pope Benedict XVI plans to participate and an envoy of Francis is celebrating a simultaneous Mass at the Fatima shrine itself.

The ritual is of deep spiritual importance to many Catholics and a source of fascination to many others. It deals with some of the more controversial aspects of the Catholic faith: purported visions of the Madonna, prophesies of hell, Soviet communism and the death of a pope, and whether the prophesies contained in the so-called “secrets of Fatima” have already been fulfilled or not.

The Mass is Francis’ latest effort to rally prayers for an end to the war while keeping open options for dialogue with the Russian Orthodox Church and its influential leader, Patriarch Kirill. Francis has yet to publicly condemn Russia by name for its invasion, though his denunciations have grown increasingly strident and outraged in recent weeks.

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The Fatima story dates to 1917, when according to tradition, Portuguese siblings Francisco and Jacinta Marto and their cousin Lucia said the Virgin Mary appeared to them six times and confided to them three secrets. The first two described an apocalyptic image of hell, foretold the end of World War I and the start of World War II, and the rise and fall of Soviet communism. The children were aged between 7 and 10 at the time.

In 2000, the Vatican disclosed the long-awaited third secret, describing it as foretelling the May 13, 1981, assassination attempt against St. John Paul II in St. Peter’s Square.

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According to later writings by Lucia, who became a nun and died in 2005, Russia would be converted and peace would reign if the pope and all the bishops of the world consecrated Russia to the “Immaculate Heart of Mary.” Lucia later claimed that John Paul fulfilled that prophesy during a Mass on March 25, 1984, exactly 38 years ago Friday, even though he never specified Russia in the prayer.

The text of Francis’ prayer Friday appears to correct that 1984 omission, reading: “Therefore, Mother of God and our Mother, to your Immaculate Heart we solemnly entrust and consecrate ourselves, the Church and all humanity, especially Russia and Ukraine.” It adds: “Grant that war may end and peace spread throughout the world.”

For some traditionalist Catholics, Francis’ pronunciation of Russia in the prayer, as well as his invitation for all the world’s bishops to join him, finally fulfills the original Fatima prophesy. Some quibble that he has added in Ukraine, while others point to the fact that the original call for Russia’s “conversion” — presumably to Catholicism — might well have been a priority for the Catholic Church in 1917 but is not a focus of the Vatican’s evangelization project now.

Soon after Francis announced his plans to hold the consecration prayer, Patriarch Kirill announced he, too, was inviting the Russian Orthodox to direct prayers to the Mother of God. Kirill has called for peace but he has also seemingly justified the invasion by invoking Russia and Ukraine as “one people” and describing the conflict as a “metaphysical” battle.

The Rev. Stefano Caprio, a former Catholic missionary in Russia and a professor of Russian history and culture at the Pontifical Oriental Institute in Rome, said Kirill is hardly the most hawkish of Russian patriarchs and is presumably under pressure to toe the Kremlin’s official line. But in comments to reporters this week, Caprio noted that the Catholic and Orthodox prayers being offered up Friday carry some significant ambiguities.

“The problem is that these are two different interpretations: The Madonna who favors peace, and the Madonna who supports the war,” he said.