17 What has just been said about the lawful variety that can exist in the Church must also be taken to apply to the differences in theological expression of doctrine. In the study of revelation East and West have followed different methods, and have developed differently their understanding and confession of God's truth. It is hardly surprising, then, if from time to time one tradition has come nearer to a full appreciation of some aspects of a mystery of revelation than the other, or has expressed it to better advantage. In such cases, these various theological expressions are to be considered often as mutually complementary rather than conflicting. Where the authentic theological traditions of the Eastern Church are concerned, we must recognize the admirable way in which they have their roots in Holy Scripture, and how they are nurtured and given expression in the life of the liturgy. They derive their strength too from the living tradition of the apostles and from the works of the Fathers and spiritual writers of the Eastern Churches. Thus they promote the right ordering of Christian life and, indeed, pave the way to a full vision of Christian truth. All this heritage of spirituality and liturgy, of discipline and theology, in its various traditions, this holy synod declares to belong to the full Catholic and apostolic character of the Church. We thank God that many Eastern children of the Catholic Church, who preserve this heritage, and wish to express it more faithfully and completely in their lives, are already living in full communion with their brethren who follow the tradition of the West.
Source: Unitatis Redintegratio (Vatican.va)