The Ruthenian Uniate Church (; ; ; ) was a particular church of the Catholic Church in the territory of the Polish–Lithuanian Commonwealth. It was created in 1595/1596 by those clergy of the Eastern Orthodox Church who subscribed to the Union of Brest. In the process, they switched their allegiances and jurisdiction from the Ecumenical Patriarchate of Constantinople to the Holy See. It had a single metropolitan territory — the Metropolis of Kiev, Galicia and all Ruthenia. The formation of the church led to a high degree of confrontation among Ruthenians, such as the murder of the hierarch Josaphat Kuntsevych in 1623. Opponents of the union called church members "Uniates" although Catholic documents no longer use the term due to its perceived negative overtones. In 1620, these dissenters erected their own metropolis — the "Metropolis of Kiev, Galicia and all Ruthenia".
Background
Kievan Rus' is an ecclesiastical and cultural description of the eastern Rus' lands during the high Middle Ages. The Greek and Latin equivalents of Rus' were Rosija and Ruthenia. It had been an empire rather than a nation state since it had many principalities and some non Slavic people. By the time of the Union of Brest, these names covered all the Eastern Slav peoples and lands, regardless of whether they belonged politically to the Grand Duchy of Moscow, the Grand Duchy of Lithuania, the Crown of Poland or the Crown of Hungary. The Rus' accepted Christianity in its Byzantine form at the same time as the Poles accepted it in its Latin form; Lithuanians largely remained pagan to the late Middle Ages before their nobility embraced the Latin form upon the political union with the Poles. The eastward expansion of the Grand Duchy of Lithuania had been facilitated by amicable treaties and inter-marriages of the nobility when faced with the external threat of the Mongol invasion of Kievan Rus'. Ethnically, the Catholics of the Commonwealth were Poles, Germans and Lithuanians.
During the Protestant Reformation of the 16th century, both the Catholic Church in the Commonwealth and the Ruthenian Church underwent a period of decay. The Ruthenian Church was the church of a people without statehood. The Poles considered the Ruthenians as a conquered people. Over time, the Lithuanian military and political ascendancy did away with the Ruthenian autonomies. The disadvantageous political status of the Ruthenian people also affected the status of their church and undermined her capacity for reform and renewal. Furthermore, they could not expect support from the Mother Church in Constantinople or from their co-religionists in Moscow. Thus the Ruthenian church was in a weaker position than the Catholic Church in the Commonwealth.
Decay of the Ruthenian Church in the Commonwealth
Both the Catholic and the Ruthenian churches suffered from the policy of nominations to higher benefices by the King, the indifference of the nobility, and a low state of clerical education and discipline. The monarchs used nominations to bishoprics as rewards to faithful civil servants. After Metropolitan Joseph II Soltan (1509–1522), the names of the great families are missing among the nominees to the bishoprics. While the great families could have obtained the nominations had they cared, since they did not, the nominees came from the poorer gentry and from the burghers. Prelates continued to live the style of life they were used to as laymen: they took part in raids and carried on trade and money lending. The Ruthenian Church had no cathedral chapters to make up for the deficiencies of the bishops.
The level of education of the Ruthenian peasantry had been falling during the sixteenth century.<ref>Ploshchanskii, Proshloe, Volume I, p10, shows it for the Diocese of Kholm.</ref> This was one of the main reasons for ecclesiastical decay and one of the impediments to renewal. For the common people, their religion was ritualism; attendance was often limited to baptism and church burial.