Cullmann leaves an impressive body of theological work: studies on the New Testament, on early church history and, running like a red thread through all of this, his many writings on ecumenical subjects. More important still was his activity as a teacher of theology. Though on first sight he may have given the impression of being wholly preoccupied with his own concerns, he was in fact extremely attentive to his students.

'Adviser to three Popes'
Everything marked Cullmann out for ecumenical commitment; he came from Strasbourg, the city of the Reformation figure Martin Bucer, he was bilingual and he was passionate about the "essence" of the Christian faith. He became involved in interconfessional talks as early as the 1920s. Without repudiating his Lutheran background, he taught for many years at the Reformed Faculty in Basle. After the Second World War his teaching activities extended to Paris and Rome. The time spent at the Waldensian Faculty in Rome gave him the opportunity to make many Roman Catholic contacts. His uncomplicated, salvation history-oriented theology was also well-received in Rome. His book "Peter - Disciple, Apostle, Martyr" (1952) paved the way for an objective discussion on a sensitive subject in relations between the confessions. At a time when contacts at the highest level were unusual, he was received by the Popes Pius XII, John XXIII, and above all, Paul VI. Karl Barth used to say teasingly, "Oscar, on your gravestone it will say ‘Here lies the adviser to three Popes’". Tease he might, but years later, when times had changed, Barth himself made a high-profile visit to Rome. Cullmann was personally invited as an observer to the Second Vatican Council and his voice was heeded by many. His conversations with Paul VI gave rise to the plan for an ecumenical institute in Jerusalem.

Unity in Diversity
Cullmann always tried to place his New Testament scholarship at the service of the ecumenical movement. An important contribution to greater mutual openness between the churches was his suggestion that - following the example in Paul - the separated churches should take up a collection for one another (1958) , a suggestion that has since been adopted in many places, notably in connection with the Week of Prayer for Christian Unity. Increasingly, as he grew older, he focussed his attention almost exclusively on the ecumenical movement. In his widely acclaimed late work "Unity through Diversity A (1986) he developed his vision of Athe unity we seek". Starting from a biblical basis, he went on to plead for a form of unity that would be structured enough to allow for common witness, while leaving plenty of room for diversity. At an age when many people would have long since stopped writing, he continued untiringly to work on this concept in contact with others. These reflections, together with his last work on prayer, are no doubt his true legacy to the churches.