Immediately after the schism with Rome in 1870, the Old Catholic theologians dedicated themselves to a reunion of the Christian churches. The Conferences of Reunion in Bonn in 1874 and 1875 convoked by von Döllinger who was the source of inspiration and a guide of the Old Catholic Movement, are famous. Representatives of the Orthodox, Anglican and Lutheran Churches were invited. The aim was to discuss the denominational differences in view of a theological consensus as the ground for restoring the church communion. The participants choose another way to restore the Catholic Church communion as Rome has done: it influenced the climate. The Conferences did not have an immediate measurable effect, but still set the course for the later Old Catholic involvement in ecumenical affairs. The basic assumptions for participation were the following principles:
The acceptance of the Christological dogmata's of Nicea and Chalcedon; Christ's foundation of the Church; the Holy Bible, the doctrine of the undivided Church and the Church fathers of the first ten centuries as the genuine sources of belief; and as criterion the famous sentence of Vincentius of Lerinum: "id teneamus, quod ubique, semper et ab omnibus creditum est " (The true faith is what everywhere, always and by everybody has been believed.) as a preferred method for historical research.
Reunion of the Churches had to be based on a re-actualization of the decisions of faith made by the undivided Church. One may conclude that this option implies a hermeneutical theological approach by which the fundamental decisions of the Councils and the early Church structure are accepted in their importance for the actual situation. In that way the original unity of the Church could be made visible again. According to these principles the later bishops and theologians of the Old Catholic Churches stayed in contact with (Russian) Orthodox and Anglican representatives in order to restore Church union.
Old Catholic involvement in the multilateral ecumenical movement formally began with the participation of two bishops, from the Netherlands and Switzerland, at the Lausanne Faith and Order (F&O) conference (1927). This side of ecumenism has always remained a major interest for Old Catholics, who have never missed an F&O conference. Old Catholics also participate in other activities of the WCC and of national councils of churches. The OCC believes the unity which the ecumenical movement seeks for the churches is one which needs to exist as a reconciled diversity of all, rooted in the common faith and order of the early church of the first centuries. To the ongoing study process of Faith and Order Christendom owes a number of initiatives that could lead to a breakthrough of stalemates. By its active participation in the ecumenical movement since its very beginning then, the OCC demonstrates its belief in the necessity of the continuation of this work.
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