18. Every day I have a growing desire to go over the history of the Churches in order to write, at last, a history of our unity and thus return to the time when, after the death and Resurrection of the Lord Jesus, the Gospel spread to the most varied cultures and a most fruitful exchange began which still today is evidenced in the liturgies of the Churches. Despite difficulties and differences, the letters of the Apostles (cf. 2 Cor 9:11 - 14) and of the Fathers(³⁸) show very close, fraternal links between the Churches in a full communion of faith, with respect for their specific features and identity. The common experience of martyrdom, and meditation on the acts of the martyrs of every church, sharing in the doctrine of so many holy teachers of the faith, in deep exchange and sharing, strengthen this wonderful feeling of unity.(³⁹) 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 marvelous 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.(⁴⁰) The first councils are an eloquent witness to this enduring unity in diversity.(⁴¹)

Even when certain dogmatic misunderstandings became reinforced -- often magnified by the influence of political and cultural factors -- leading to sad consequences in relations between the Churches, the effort to call for and to promote the unity of the Church remained alive. When the ecumenical dialogue first began, the Holy Spirit enabled us to be strengthened in our common faith, a perfect continuation of the apostolic kerygma, and for this we thank God with all our heart.(⁴²) Although in the first centuries of the Christian era conflicts were already slowly starting to emerge within the body of the Church, we cannot forget that unity between Rome and Constantinople endured for the whole of the first millennium, despite difficulties. We have increasingly learned that it was not so much an historical episode or a mere question of pre - eminence that tore the fabric of unity, as it was a progressive estrangement, so that the other's diversity was no longer perceived as a common treasure, but as incompatibility. Even when the second millennium experienced a hardening of the polemics and the separation, with mutual ignorance and prejudice increasing all the more, nonetheless constructive meetings between church leaders desirous of intensifying relations and fostering exchanges did not cease, nor did the holy efforts of men and women who, recognizing the setting of one group against the other as a grave sin, and being in love with unity and charity, attempted in many ways to promote the search for communion by prayer, study and reflection, and by open and cordial interaction.(⁴³) All this praiseworthy work was to converge in the reflections of the Second Vatican Council and to be symbolized in the abrogation of the reciprocal excommunications of 1054 by Pope Paul VI and the Ecumenical Patriarch Athenagoras I.(⁴⁴)