49 A valuable result of the contacts between Christians and of the theological dialogue in which they engage is the growth of communion. Both contacts and dialogue have made Christians aware of the elements of faith which they have in common. This has served to consolidate further their commitment to full unity. In all of this, the Second Vatican Council remains a powerful source of incentive and orientation. The Dogmatic Constitution Lumen Gentium links its teaching on the Catholic Church to an acknowledgment of the saving elements found in other Churches and Ecclesial Communities. It is not a matter of becoming aware of static elements passively present in those Churches and Communities. Insofar as they are elements of the Church of Christ, these are by their nature a force for the re-establishment of unity. Consequently, the quest for Christian unity is not a matter of choice or expediency, but a duty which springs from the very nature of the Christian community. In a similar way, the bilateral theological dialogues carried on with the major Christian Communities start from a recognition of the degree of communion already present, in order to go on to discuss specific areas of disagreement. The Lord has made it possible for Christians in our day to reduce the number of matters traditionally in dispute.
Source: Ut Unum Sint (Vatican.va)