Catholic vs. Orthodox Slavs

From Poland: The First Thousand Years, by Patrice M. Dabrowski (Cornell University Press, 2014), Kindle pp. 231-235:

The war with Muscovite Russia was hardly over. Despite the accomplishments of the valiant Transylvanian [Stefan Batory], Polish-Russian relations had yet to enter into their most interesting—indeed, most incredible—phase. In the interim, another development took place, one that would have important repercussions for the battle not only for territory but also for the hearts and minds of the borderland inhabitants.

More precisely, this new development represented a war for souls. At the same time that Poland-Lithuania and Muscovy were vying for control of the Rus’ principalities, questions of jurisdiction over the Orthodox population of Eastern Europe generated sparks. This was the world of the Greek Church, adherents of Christianity in its Byzantine (that is, Eastern) rite.

Byzantine Christianity differed from the Church of Rome in a number of ways, not all of them doctrinal. Whereas in Roman Catholicism the high church language was Latin, there was no one single high church language in the Greek world: the Slavic lands had been given their own church language by the earliest missionaries to the Slavs, Cyril and Methodius. This language came to be known as Old Church Slavonic. Distinct from the spoken vernaculars of the region, it was nonetheless for the most part comprehensible to the population.

The relationship of the church and state in the East was also different than in the West. Following the pattern of Byzantium, the Eastern Church pragmatically subordinated itself to the authority of the state in which it functioned. Another seemingly obvious distinction: the Eastern churches did not owe allegiance to the pope in Rome but, rather, acknowledged the patriarch of Constantinople. After the fall of Constantinople in 1453, the position of the Greek Church was much diminished. This allowed for some jockeying within Eastern Christendom, especially in the East Slavic lands, where the majority of the faithful resided and the religion flourished.

To be sure, even before the Ottomans moved into Byzantium, not all was well in the Eastern Greek world further north. This in part was the result of the fact that, from its inception, the head of the Greek Church in the Rus’ lands had been the metropolitan of Kyiv. The shift of state borders that resulted in the Greek faithful residing in different states complicated the ecclesiastical picture and led various clergymen to vie with each other for influence over the faithful of Eastern Europe. To give one example: the Bulgarian clergyman who was chosen as metropolitan of the Ruthenian lands in 1415 soon found himself excommunicated by the patriarch of Constantinople, whose mind had been poisoned by the metropolitan of Moscow, who wanted this position for himself. Not until 1458 was Poland-Lithuania able to establish an independent Kyivo-Halych metropolitanate for its Orthodox population.

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Those in the Commonwealth realized that they needed to counteract such moves. Essentially there were two options. They could either establish an autocephalous Orthodox church for the country or bring about church union—here, union with what was still the biggest force in Christianity: the Church in Rome.

The latter option won out, in part because the Church of Rome had made similar efforts in the past. First attempted in Constance, union between the Roman and Greek Churches had been achieved at the Council of Florence (1439), although nothing ultimately came of it (it is this attempt at union, incidentally, that led to the formation of an autocephalous Orthodox church in Moscow). Yet another sign that union was the direction favored by the Vatican was that, as early as 1573, a Greek College was opened in Rome as well as a Congregation for Eastern Churches.

The Commonwealth, thus, was convinced to work toward union and capitalized on a desire among Commonwealth clergymen not to subordinate themselves to Muscovy—in particular, not to send their financial dues there. This became visible in the synods that took place in the town of Brest, along the internal Polish-Lithuanian border, at the end of the sixteenth century. The Greek clergy decided to support the idea of union—with qualifications. While they would recognize the authority of the pope in Rome, they were not ready to make many changes that would affect the look and feel of their religion. They were allowed to retain their distinctive Eastern rite: the liturgy in Church Slavonic, as well as other traditions, including the marriage of the clergy. A selling point for the Orthodox bishops was a further advantage specified in the act of union: they were to be admitted into the Senate of the Commonwealth, on par with the Roman Catholic bishops.

This Union of Brest, as the 1596 agreement was called, produced a new phenomenon in the Commonwealth: so-called Uniates. These were Eastern-rite Catholics, in official parlance members of the Greek-Catholic Confession of the Slavonic Rite. In other words, while they retained their traditional Eastern rite and practices, they were part of the Catholic Church.