Many Roman Catholics are barely aware of the presence in their midst of Catholics who are not of the Latin or Roman liturgical tradition. These Catholics constitute a small percentage of the 1.1 billion Catholics in the world, which accounts for their relative anonymity. However, such Eastern Catholics are a vibrant part of the Church and represent the ancient traditions of the Christian East which were largely lost to the Catholic Church in 1054 AD. In that unfortunate year Eastern Orthodox Christians, in the person of the Patriarch of Constantinople, and Latin Christians, in the person of the Supreme Pontiff, broke their ecclesiastical communion. With the exception of Maronite Catholics, Eastern Catholics are Christians who at some point in history returned to communion with the Holy See from the traditions and Churches of the East. They are thus usually identified along national or ethnic lines, as are the Eastern Churches from which they came. (see FAQ "Catholic Rites and Churches")
As bridges to the Christian East not in communion with Rome, the Church places great value on the ecumenical role which Eastern Catholics can play. The Second Vatican Council, the ecumenical documents of the Holy See, and the writings of the Holy Father, call on Eastern Catholics to preserve their own traditions, both for their own sake and for the ecumenical value they represent in relations with the Orthodox and other Eastern Churches. The Holy See has also taken care to speak clearly of the status of Eastern Catholics, preserving both their freedom of governance and their necessary submission to the supreme authority of the Apostolic See.
Every Catholic belongs to a specific ritual Catholic Church, with an identifiable hierarchy, at the head of which is usually a Patriarch. Membership is accomplished at the time of baptism. According to the Code of Canons of the Eastern Churches (Pope John Paul II, 1990) canon 27,
A group of faithful united by a hierarchy according to the norm of law which the supreme authority of the Church expressly or tacitly recognizes as sui iuris(of its own right) is called in this Code a Church sui iuris.
One can thus speak of the Roman or Latin Church. It has a hierarchy, its own mechanisms of governance under the Patriarch of the West, laws set out in the 1983 Code of Canon Law, and is ultimately subject to the Supreme Pontiff, who in this case is also Patriarch. Likewise, one can speak of an Eastern Catholic Church, such as the Ukrainian Catholic Church, which has an identifiable hierarchy under the Patriarch of Lvov, Ukraine, is governed by its own law, under the aforementioned Code of Canons of the Eastern Churches, and is ultimately subject to the Supreme Pontiff, as every Catholic Church is (Code of Canons of the Eastern Churches, canons 43-48). Thus, when speaking of Eastern Catholics it is correct to speak of them as belonging to Eastern Catholic Churches, and as individuals to specific Eastern Catholic Churches.
A Rite is a specific form or way to celebrate the Eucharistic and sacramental liturgies of the Church. When the Gospel was brought to different peoples, its essential sacramental elements were inculturated into those societies through different ritual forms, so that they would be meaningful and understandable to them while expressing the divine mysteries they contained. There is thus more than one Rite in the Church, although because of its size most Catholics and non-Catholics associate the Latin or Roman Rite with Catholicism. The Code of Canons of the Eastern Churches describes rites this way in canon 28,
1. A rite is the liturgical, theological, spiritual and disciplinary patrimony, culture and circumstances of history of a distinct people, by which its own manner of living the faith is manifested in each Church sui iuis.
2. The rites treated in this code, unless otherwise stated, are those which arise from the Alexandrian, Antiochene, Armenian, Chaldean and Constantinopolitan traditions.
Since several Eastern Catholic Churches can share the same "liturgical, spiritual and disciplinary patrimony," for example, the Constantinopolitan or Byzantine (see FAQ mentioned above), and share them with Churches not in communion with Rome, the expression "Eastern Rites" only applies in the limited context of the various Eastern historical, liturgical and theological patrimonies. Eastern Catholics belong to Churches, therefore, not Rites.
Sister Churches. It has become quite common to speak of Sister Churches, both in connection with the relation of the separated Churches of the East (e.g. the Orthodox) with Rome, as well as the Eastern Catholic Churches with Rome. This is possible because all the Churches in question have a valid hierarchy. (This term can thus never be applied to the ecclesial bodies derived from the Reformation, as they lack a valid hierarchy.)
While useful ecumenically, the term is only valid within certain theological limits, which were specified in 2000 by the Congregation for the Doctrine of the Faith. In this instruction the Holy See makes clear that the use of this expression, with respect to Rome in particular, does not derogate from the prerogatives given in Divine Law to the Apostolic See. (see Note on the Expression "Sister Churches")
Thus, Rome as the See of Peter is the Mother Church of Christendom. Considered solely as a diocese she is a sister of every other local Church, since each local Church (with a bishop, presbyterate and diaconate representing Christ the Head, and the people His Body) is fully a sign of the whole Church, the whole Mystical Christ. Also, each ritual Church (Latin, Ukrainian, Byzantine, Maronite, Syro-Malabar, Coptic etc.) can be considered a sister of every other ritual Church.
Some have suggested that Rome cannot be both a sister and a mother. The language is not only NOT inconsistent but very Scriptural. Thus, in the Song of Songs the Bridegroom calls his Bride his sister (Song 4:9-10). It is the language of love, that is of a deeply shared spiritual communion. Likewise, the Church is the Bride of Christ, but also His Body. Different human realities convey different aspects of the mystery which is the Church. They complement, not contradict. It is thus true that the Roman Church is both sister to all Catholic Churches and Mother of them all. And in the sense explained by the Congregation, she is "sister" to the ancient Christian Churches of the East, as well.