“Could we not also have prayed along with them?”

Bonhoeffer was clearly charmed by the place, but as a Protestant pastor he was not completely at ease with everything he saw and experienced. “The Catholic Advent seems somewhat strange to me,” he wrote to Bethge. At Finkenwalde, the Lord’s Supper had been celebrated once each week. At Ettal, Bonhoeffer could go to Mass and share in the prayers and readings, but, as he was not a member of the Catholic Church, he could not partake of the bread and wine at communion. “I am longing for the Lord’s Supper,” he said. Still, Bonhoeffer’s presence at what he called “quite a wonderful Mass” did bear witness to a kind of broken unity, a sanctorum communio not yet fully realized in the visible church of the undivided Christ here and now. Several weeks before Bonhoeffer arrived in Ettal, as war raged across Europe, Pope Pius XII had issued a Motu Proprio calling for a “crusade of prayer,” inviting Catholics around the globe to join in a prayer for world peace. In a letter to Bethge, Bonhoeffer referred to the Pope’s decree: “Today the pope has ordered a prayer for peace in the whole church. Could we not also have prayed along with them? I did.”

Source: Timothy George  -  "Bonhoeffer at Ettal: Advent", First Things, 12 Dec 2016, https://www.firstthings.com/web-exclusives/2016/12/bonhoeffer-at-ettal-advent-1940