64 In its great plan for the re-establishment of unity among all Christians, the Decree on Ecumenism also speaks of relations with the Churches and Ecclesial Communities of the West. Wishing to create a climate of Christian fraternity and dialogue, the Council situates its guidelines in the context of two general considerations: one of an historical and psychological nature, and the other theological and doctrinal. On the one hand, this Decree affirms: "The Churches and Ecclesial Communities which were separated from the Apostolic See of Rome during the very serious crisis that began in the West at the end of the Middle Ages, or during later times, are bound to the Catholic Church by a special affinity and close relationship in view of the long span of earlier centuries when the Christian people lived in ecclesiastical communion". On the other hand, with equal realism the same Document states: "At the same time one should recognize that between these Churches and Communities on the one hand, and the Catholic Church on the other, there are very weighty differences not only of a historical, sociological, psychological and cultural nature, but especially in the interpretation of revealed truth".
Source: Ut Unum Sint (Vatican.va)