This church division took place during the Reformation in the West in the 16th century. Like other schisms, this one does not yield to simple analysis or explanation. The Reformation was a mixture of theology, ecclesiology, politics, and nationalism, all of which led to breaks in fellowship and created institutional alienation between Christians throughout Western Christendom. In one sense it was a separation, especially a reaction against the rigid juridical structures of medieval Roman Catholicism and its claim to universal truth and jurisdiction. In another sense, however, the Reformation was an evangelical and ecumenical renewal of the church as the Body of Christ, an attempt to return to the apostolic and patristic sources in order, according to John Calvin, “to recover the face of the ancient Catholic Church.” All the Continental reformers sought to preserve and reclaim the unity of the church.

Once the separation between the Roman Catholic and new Protestant churches was complete, people on both sides tried to restore unity. Roman Catholics such as Georg Witzel and George Cassander developed proposals for unity, which all parties rejected. Martin Bucer, celebrated promoter of church unity among the 16th-century leaders, brought Martin Luther and his colleague Philipp Melanchthon into dialogue with the Swiss reformer Huldrych Zwingli at Marburg, Germany, in 1529. In 1541 John Calvin (who never ceased to view the church in its catholicity), Bucer, and Melanchthon met with Gasparo Cardinal Contarini and other Roman Catholics at Ratisbon (now Regensburg, Germany) to reconcile their differences on justification by faith, the Lord’s Supper, and the papacy. Another attempt was made in 1559, when Melanchthon and Patriarch Joasaph II of Constantinople corresponded, with the intention of using the Augsburg Confession as the basis of dialogue between Lutheran and Eastern Orthodox Christians. On the eve of the French wars of religions (1561), Roman Catholics and Protestants conferred without success in the Colloquy of Poissy. It would seem that the ecumenical projects of theologians and princes in 16th-century Europe failed unequivocally, but they kept alive the vision and the hope.