Martin Bucer

These efforts came to a culmination in the 1541 Imperial Diet at Regensburg (Ratisbon). Henry VIII sent Bishop Stephen Gadiner of Winchester, Rome sent the irenic Cardinal Contarini. MacCulloch writes, “When introduced to Bucer, [Contarini] observed, ‘How great will be the fruit of unity, and how profound the gratitude of all mankind’. Bucer replied equally graciously: ‘Both sides have failed. Some of us have overemphasized unimportant points, and others have not adequately reformed obvious abuses. With God’s will we shall ultimately find the truth.'”

Not everyone wanted Regensburg to succeed: “some of the Emperor’s own princes were not anxious to see the Habsburg family’s problems solved, even less so the King of France, who would have been a necessary party to any final agreement.” But the politicians weren't the cause of the failure; the theologians were: “Contarini could not give ground on the eucharistic doctrine of transubstantiation; the Protestants were not prepared to say that confession to a priest was necessary. Their measure of agreement on justification in the Regensburg Book was therefore irrelevant. Then messages from both Rome and Luther in Wittenberg made it quite clear that even that would not be accepted.”

Source: Martin Bucer  -  Martin Bucer, Regensburg Diet, 1541, as quoted by Diarmaid MacCulloch in "Europe's House Divided", as quoted by Peter Leithart, "Ecumenism in the Sixteenth Century", First Things, 6 Feb 2017, https://www.firstthings.com/blogs/leithart/2017/02/ecumenism-in-the-sixteenth-century