48 The relationships which the members of the Catholic Church have established with other Christians since the Council have enabled us to discover what God is bringing about in the members of other Churches and Ecclesial Communities. This direct contact, at a variety of levels, with pastors and with the members of these Communities has made us aware of the witness which other Christians bear to God and to Christ. A vast new field has thus opened up for the whole ecumenical experience, which at the same time is the great challenge of our time. Is not the twentieth century a time of great witness, which extends "even to the shedding of blood"? And does not this witness also involve the various Churches and Ecclesial Communities which take their name from Christ, Crucified and Risen? Such a joint witness of holiness, as fidelity to the one Lord, has an ecumenical potential extraordinarily rich in grace. The Second Vatican Council made it clear that elements present among other Christians can contribute to the edification of Catholics: "Nor should we forget that whatever is wrought by the grace of the Holy Spirit in the hearts of our separated brothers and sisters can contribute to our own edification. Whatever is truly Christian never conflicts with the genuine interests of the faith; indeed, it can always result in a more ample realization of the very mystery of Christ and the Church". Ecumenical dialogue, as a true dialogue of salvation, will certainly encourage this process, which has already begun well, to advance towards true and full communion.
Source: Ut Unum Sint (Vatican.va)