Ukrainian Greek Catholic Church in the context of "Ruthenian Uniate Church"

The Eastern Catholic Churches or Oriental Catholic Churches, also known as the Eastern-Rite Catholic Churches, Eastern Rite Catholicism, or simply the Eastern Churches, are 23 Eastern Christian autonomous (sui iuris) particular churches of the Catholic Church in full communion with the pope in Rome. Although they are distinct theologically, liturgically, and historically from the Latin Church, they are all in full communion with it and with each other. Eastern Catholics are a minority within the Catholic Church; of the 1.3 billion Catholics in communion with the pope, approximately 18 million are members of the Eastern churches. The largest numbers of Eastern Catholics are found in Eastern Europe, Eastern Africa, the Middle East, and India. As of 2022, the Syro-Malabar Church is the largest Eastern Catholic Church, followed by the Ukrainian Greek Catholic Church.

With the exception of the Maronite Church, the Eastern Catholic Churches are groups that, at different points in the past, used to belong to the Eastern Orthodox Church, the Oriental Orthodox churches, or the Church of the East; these churches underwent various schisms through history. Eastern Catholic Churches that were formerly part of other communions have been points of controversy in ecumenical relations with the Eastern Orthodox and other non-Catholic churches. The five historic liturgical traditions of Eastern Christianity, namely the Alexandrian Rite, the Armenian Rite, the Byzantine Rite, the East Syriac Rite, and the West Syriac Rite, are all represented within Eastern Catholic liturgy. On occasion, this leads to a conflation of the liturgical word "rite" and the institutional word "church". Some Eastern Catholic jurisdictions admit members of churches not in communion with Rome to the Eucharist and the other sacraments.

Liturgy is the customary public ritual of worship performed by a religious group. As a religious phenomenon, liturgy represents a communal response to and participation in the sacred through activities reflecting praise, thanksgiving, remembrance, supplication, or repentance. It forms a basis for establishing a relationship with God or the divine.

Technically speaking, liturgy forms a subset of ritual. The word liturgy, sometimes equated in English as "service", refers to a formal ritual enacted by those who understand themselves to be participating in an action with the divine.

In the Eastern Catholic Churches, major archbishop (sometimes also styled as major archeparch) is a title for the chief hierarch ("Father and Head") of an autonomous (sui juris) particular Church that has not been "endowed with the patriarchal title". Major archbishops generally have the same rights, privileges, and jurisdiction as Eastern Catholic patriarchs, except where expressly provided otherwise, and rank immediately after them in precedence of honor.

In addition to their role governing their particular Church, major archbishops, like Eastern Catholic patriarchs, are ex officio members of the Congregation for the Oriental Churches in the Roman Curia. They are required to attend the annual general meeting of this congregation, as well as other sessions if they are visiting Rome or are otherwise able.

The Union of Brest took place in 1595 and 1596 and represented an agreement by Eastern Orthodox Churches in the Ruthenian portions of the Polish–Lithuanian Commonwealth to accept the Pope's authority while maintaining Eastern Orthodox liturgical practices, leading to the formation of the Ruthenian Uniate Church, which currently exists as the Ukrainian Greek Catholic Church and the Belarusian Greek Catholic Church.
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