The meeting between the Pope and the Patriarch has occasioned much conjecture, but this article from Rorate Caeli is the best yet.

An excerpt.

Among the many successes the mass-media attributes to Pope Francis, is the “historical meeting” with the Patriarch of Moscow, Kirill, which took place on February 12th in Havana. An event, it is written, that saw the collapse of the wall which has divided the Church of Rome from the Eastern Church for a thousand years. The importance of the meeting, according to the words of Francis himself, was not in the document – of a merely “pastoral” nature – but in the convergence towards a common destination, not political nor moral, but religious. As for the traditional Magisterium of the Church, articulated in documents, Pope Francis seems to want it substituted by a Neo-Magisterium, transmitted through symbolic events. The message the Pope aims to give is that this is a turning-point in the history of the Church. Yet it is precisely the history of the Church we need to start with to understand the significance of the event. Historical inaccuracies are indeed many and need to be corrected, since it’s exactly upon false historians that doctrinal deviations are frequently built.

First of all, it is not true that a thousand years of history separate the Church of Rome from the Patriarchate of Moscow, seeing that this came about only in 1589. In the preceding five centuries, and even before that, Rome’s Eastern interlocutor was the Patriarch of Constantinople.

During the Second Vatican Council, on January 6th 1964, Paul VI met Patriarch Athenagoras in Jerusalem to initiate “ecumenical dialogue” between the Catholic world and the Orthodox world. This dialogue could not move forward because of the Orthodox thousand-year opposition to the Primate of Rome. Paul VI himself, admitted this in a speech to the Secretariat for the Unity of Christians on April 28th 1967, affirming: “The Pope, we know this well, is without doubt the greatest obstacle on the path of ecumenism” (Paul VI, Teachings, VI, pp.192-193).

The Patriarchate of Constantinople constituted one of the five principle Sees of Christianity established by the Council of Chalcedon in 451. The Byzantine Patriarchs sustained however, that after the fall of the Roman Empire, Constantinople, See of the reborn Roman Empire in the East, should have become the religious capital of the world. Canon 28 of the Council of Chalcedon, abrogated by Leo the Great, contains the seed of the entire Byzantine Schism, as it attributes to the Roman Pontiff’s supremacy a political and not divine foundation. For this, in 515, Pope Hormisdas (514-523) made the Eastern Bishops sign a Formula of Union, in which they acknowledged their submission to the Chair of Peter (Denz-H, n.363).

Between the V and X centuries, while the West was affirming the distinction between spiritual authority and temporal power, in the East, in the meantime, so-called “Caesaropapism” was born, in which the Church was de facto subordinated to the Emperor who considered himself the head, inasmuch as delegated by God, in both the ecclesiastical and secular field. The Patriarchs of Constantinople were de facto reduced to functionaries of the Byzantine Empire and continued to ferment a radical aversion for the Church of Rome.

After the first rupture, caused by Patriarch Photios in the IX century, the official schism occurred on July 16th 1054, when the Patriarch Michael Cerularius declared Rome fallen into heresy for reason of the “Filioque” and other pretexts. The Roman legates then deposed the sentence of excommunication against him on the altar of Hagia Sophia in Constantinople. The Princes of Kiev and Moscow, converted to Christianity in 988 by St. Vladimir, followed the Patriarchs of Constantinople into schism, and acknowledged their religious jurisdiction.

The discords seemed insurmountable but an extraordinary event occurred on July 6th 1439 in the Florentine Cathedral of Santa Maria del Fiore, when Pope Eugene IV, solemnly announced, with the Bull Laetentur Coeli (“that the heavens rejoice”) the recomposition of the schism between the Churches of the East and the West.

During the Council of Florence (1439), in which the Emperor of the East, John VIII Palaiologos and the Patriarch of Constantinople Joseph II participated, an agreement was reached on all the problems, from the Filioque to the Roman Primacy. The Pontifical Bull concluded with this solemn dogmatic definition, signed by the Greek Fathers: “We define that the Holy Apostolic See and the Roman Pontiff have primacy over the entire universe; that the same Roman Pontiff is the successor of Blessed Peter, Prince of the Apostles; he is the authentic Vicar of Christ, Head of the entire Church, Father and Doctor of all Christians; that Our Lord Jesus Christ has transmitted to him, in the person of Blessed Peter, full power to nourish, sustain and govern the Universal Church, as is attested also in the Acts of the Ecumenical Councils’ and in the Sacred Canons” (Conciliorum Oecumenicorum Decreta, Centro Editoriale Dehoniano, Bologna 2013, pp. 523-528). This was the only true historical embrace between the two Churches in the course of the last millennium.

Among the most active participants at the Council of Florence, was the Metropolitan of Kiev and all Russia, Isidore. As soon as he returned to Moscow, he made a public announcement on the reconciliation under the Roman Pontiff’s authority, but the Prince of Moscow, Vasily The Blind, declared him a heretic and substituted him with a bishop subject to himself. This action marked the beginning of the Church of Moscow’s autocephaly, independent not only from Rome but also from Constantinople.