Sister Churches (ecclesiology)

Sister churches is a term used in 20th-century ecclesiology to describe ecumenical relations between the Roman Catholic Church and the Eastern Orthodox Churches, and more rarely and unofficially, between the Roman Catholic Church and the Anglican communion. The term is also used among Protestants to refer to different denominations of the same religious tradition.

The expression, allegedly in use among the Orthodox since the fifth century among the "patriarchal sister Churches", appeared in written form in two letters of the Metropolitan Nicetas of Nicomedia (1136) and the Patriarch John Camaterus (in office from 1198 to 1206), in which they protested that Rome, by presenting herself as mother and teacher, would annul their authority. In their view, Rome was only the first among sister churches of equal dignity, see first among equals. According to this idea of Pentarchy, there are five Patriarchs at the head of the Church, with the Church of Rome having the first place of honor among these patriarchal sister churches. According to the Congregation for the Doctrine of the Faith, however, no Roman pontiff ever recognised this Orthodox equalization of the sees or accepted that only a primacy of honor be accorded to the See of Rome.

In modern times, the expression "sister Churches" first appeared in John XXIII's letters to the Orthodox Patriarch of Constantinople, Athenagoras I. In his letters, the pope expressed the hope of seeing the unity between the sister churches re-established in the near future. Later the term appeared in a "Joint Declaration" between Pope Paul VI and Patriarch Athenagoras in 1965, representing their respective sees, Rome and Constantinople, respectively.

The Second Vatican Council adopted the expression "sister Churches" to describe the relationship between particular Churches: "in the East there flourish many particular local Churches; among them the patriarchal Churches hold first place, and of these, many glory in taking their origins from the apostles themselves. Therefore, there prevailed and still prevails among Eastern Christians an eager desire to perpetuate in a communion of faith and charity those family ties which ought to exist between local Churches, as between sisters."

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