14 For many centuries the Church of the East and that of the West each followed their separate ways though linked in a brotherly union of faith and sacramental life; the Roman See by common consent acted as guide when disagreements arose between them over matters of faith or discipline. Among other matters of great importance, it is a pleasure for this Council to remind everyone that there flourish in the East many particular or local Churches, among which the Patriarchal Churches hold first place, and of these not a few pride themselves in tracing their origins back to the apostles themselves. Hence a matter of primary concern and care among the Easterns, in their local churches, has been, and still is, to preserve the family ties of common faith and charity which ought to exist between sister Churches. Similarly it must not be forgotten that from the beginning the Churches of the East have had a treasury from which the Western Church has drawn extensively - in liturgical practice, spiritual tradition, and law. Nor must we undervalue the fact that it was the ecumenical councils held in the East that defined the basic dogmas of the Christian faith, on the Trinity, on the Word of God Who took flesh of the Virgin Mary. To preserve this faith these Churches have suffered and still suffer much. However, the heritage handed down by the apostles was received with differences of form and manner, so that from the earliest times of the Church it was explained variously in different places, owing to diversities of genius and conditions of life. All this, quite apart from external causes, prepared the way for decisions arising also from a lack of charity and mutual understanding. For this reason the Holy Council urges all, but especially those who intend to devote themselves to the restoration of full communion hoped for between the Churches of the East and the Catholic Church, to give due consideration to this special feature of the origin and growth of the Eastern Churches, and to the character of the relations which obtained between them and the Roman See before separation. They must take full account of all these factors and, where this is done, it will greatly contribute to the dialogue that is looked for.
Source: Unitatis Redintegratio (Vatican.va)