In a schism redolent of the Middle Ages, some of the most august religious leaders in the world are beginning to take sides in the bloody factions of realpolitik and war. The involvement of the princes of the Catholic and Russian Orthodox Churches in Russia’s war on Ukraine augurs a new, spiritual dimension to a conflict now more than a month old. 

Two men who have risen to the pinnacle of global faiths — Patriarch of Moscow and all Rus’ and Primate of Moscow, Kirill; and the Bishop of Rome, Pope Francis — have found themselves on opposing sides of the conflict. 

Patriarch Kirill has emerged as one of the war’s most prominent supporters, seeing in it theological drama. Pope Francis, alternatively, has pleaded for peace and has spoken of Ukrainian “martyrs.” 

The Russian Orthodox Church helmed by Patriarch Kirill is one of the largest of the Eastern Churches and numbers its adherents at 80 million. Headquartered at Moscow, it traces its spiritual genesis to the conversion of Vladimir the Great at Kiev in 988 of the common era. 

The Catholic Church helmed by Pope Francis is centered at Vatican City and is the world’s largest, with approximately 1.3 billion members. 

The split between the two religious leaders harkens to a time when kings and popes jousted and collaborated, and tsar and church together ruled the length and breadth of Russia. 

As the first land war in eight decades grinds through Ukraine, the prominent role of pontiff and patriarch, set against ghosts of empire and grievance, is once again headline news.

The reactions to the war have also spotlighted a history of schism and split between East and West, with both the secular and the faithful casting their gazes back to 1054. 

In that fateful year, the Patriarch of Constantinople, Michael Cerularius, and the Bishop of Rome, Pope Leo IX, excommunicated one another, rending the two Christian believers of two hemispheres. While relations between the Orthodox and Catholic churches have warmed, the schism remains unhealed.       

Patriarch Kirill has long been a supporter of President Putin and shares his antagonism toward the West. In 2012, the former described Mr. Putin’s electoral victory as “a miracle of God.” Since then Kremlinologists have noted a hand in glove operation between church and state. 

The patriarch detects in the war in Ukraine a “metaphysical significance” that goes beyond territory to encompass a larger spiritual struggle between East and West. Hours before bombs began to fall on Ukraine, Patriarch Kirill — who like Mr. Putin is alleged to have been a former KGB agent — went on Russian television and hailed military service as “an active manifestation of evangelical love for neighbors.” 

In 2018, the Patriarch spoke of “the ethnoses united in the great historical Rus,” endorsing the idea of a “Russkiy mir,” a Russian world that has become central to Mr. Putin’s dreams of conquest. 

Even as Patriarch Kirill and Mr. Putin fantasize about a Russian imperium, the Patriarch’s stance has alienated members of his own flock.    

In an open letter denouncing Patriarch Kirill’s position as heresy against the creed of the Church he leads, hundreds of Russian Orthodox clerics highlighted the central claims of this weltanschauung as one that envisions Russia with “a common political center (Moscow),” and “a common spiritual center (Kiev as the “mother of all Rus’’) under the joint leadership of Mr. Putin and Patriarch Kirill.

These faithful anguished by the war argue that “just as Russia has invaded Ukraine, so too the Moscow Patriarchate of Patriarch Kirill has invaded the Orthodox Church.” They “reject the ‘Russian world’ heresy and the shameful actions of the Government of Russia in unleashing war against Ukraine which flows from this vile and indefensible teaching with the connivance of the Russian Orthodox Church.” 

Concern over the Patriarch’s yoking of the cross to what many see as a war of conquest is sounding from the gilded halls of the  Vatican as well. After a March 16 video conference between the two men, the Holy See’s press office records that the Pope told the Patriarch that “once upon a time there was also talk in our churches of holy war or just war. Today we cannot speak like this.” 

Pope Francis also told the Patriarch: “The Church must not use the language of politics, but the language of Jesus.” This pushback has been echoed by Pope Francis’s subordinates as well, with the Vatican Secretary of State, Cardinal Pietro Paolin, saying, “Kirill’s words do not favor or promote an agreement. Instead, they risk heightening spirits toward an escalation and not solve the crisis peacefully.” 

The Pope has endeavored to do just that. In a dramatic moment during his weekly general audience on Wednesday, the pontiff kissed a Ukrainian flag and exclaimed, “Stop this war. Let the weapons fall silent. Stop sowing death and destruction.” 

In the days before the war began, Pope Francis broke protocol to make an appearance at the Russian Embassy. His pleas for peace went unheeded.

The relationship between the two men — Patriarch Kirill and Pope Francis — was not always this contentious. In 2016, at Havana, they became the first leaders of their respective faiths to meet since that 1054 split. They are set to convene again in June, though as war drags on that encounter is now in doubt.   

It is recorded that on the fateful July day more than a millennium ago when the churches split, a papal envoy deposited the letter of excommunication on the altar of the Hagia Sophia at what was then Constantinople and remarked “Videat Deus et judicet” — “Let God see and judge.” 

Now, the whole world is watching.