61 In view of all this, the Catholic Church desires nothing less than full communion between East and West. She finds inspiration for this in the experience of the first millennium. In that period, indeed, "the development of different experiences of ecclesial life did not prevent Christians, through mutual relations, from continuing to feel certain that they were at home in any Church, because praise of the one Father, through Christ in the Holy Spirit, rose from them all, in a marvellous variety of languages and melodies; all were gathered together to celebrate the Eucharist, the heart and model for the community regarding not only spirituality and the moral life, but also the Church's very structure, in the variety of ministries and services under the leadership of the Bishop, successor of the Apostles. The first Councils are an eloquent witness to this enduring unity in diversity". How can unity be restored after almost a thousand years? This is the great task which the Catholic Church must accomplish, a task equally incumbent on the Orthodox Church. Thus can be understood the continuing relevance of dialogue, guided by the light and strength of the Holy Spirit.
Source: Ut Unum Sint (Vatican.va)