DIETRICH BONHOEFFER was executed at dawn on 9 April 1945 - less than a month before the end of the Second World War - after Hitler had been told the extent of his involvement in the plot to overthrow him.

Bonhoeffer had been one of the most outspoken members of the Confessing Church since 1933, campaigning tirelessly against the pro-Nazi leadership of the German Evangelical Church. He attempted to rally his fellow-Lutherans against the expulsion of "non-Aryans", first from the Church, and then from the country. From 1939, he was part of the (mainly Christian) political resistance to the Nazi regime which was ruthlessly expunged after the failure of the Stauffenberg plot in July 1944 .

That Bonhoeffer should be seen, therefore, as "one of the noble company of martyrs" was recognised by the then Bishop of Chichester, George Bell, at a memorial service in Holy Trinity, Kingsway, in July 1945.

While Germans remained suspicious of Bonhoeffer's "treasonous" activity - his decision to pray and work for the defeat of their country - Bell, who had known of Bonhoeffer's commitment to peace from the ecumenical movement in the early 1930s, was in no doubt about the Christian inspiration and heroism of his resistance to evil. His murder was a clear example of odium fidei.

A likeness of Bonhoeffer, complete with limestone spectacles, has stood over the western entrance to Westminster Abbey since 1998, as one of the ten 20th-century martyrs celebrated there.

BONHOEFFER has something to offer to all strands of Anglicanism. Evangelicals love him because he set such store by the Bible, which he read every day, even in prison, and because he experienced a (sort of) conversion in his mid-twenties, turning him from an ambitious young theologian to a "hero of faith".

Liberals can applaud his open-minded engagement with the modern world, and his preparedness to ask awkward questions of traditional forms of religious language and practice. Anglo-Catholics can appreciate his awareness of the relative liturgical poverty of his native Lutheranism, pointing to the way he developed Catholic practices such as confession and meditation in his own seminary at Finkenwalde, having witnessed them at the religious communities at Mirfield and Kelham, which he visited in 1935.

He went beyond the ecumenism of his day, which was largely intra-Protestant, in admiring the Roman Catholic liturgy he encountered in Rome in Easter 1924, aged 18, and in Barcelona, where he spent a year from 1928.

He surprised his affluent, upper-middle-class and prodigiously talented family (his father was Professor of Psychology at the University of Berlin) by opting, at the age of 13, to become a theologian. He studied in the notoriously liberal Department of Theology at Berlin, before coming under the spell of the neo-orthodox Karl Barth.

His first two books, completed by the age of 24, display the richness and complexity of his ecclesiology. Sanctorum Communio turns to contemporary sociology for an understanding of the Church as transcending Ferdinand Tönnies's distinction between a "community" (Gemeinschaft, rooted in history and shared traditions), and a "society" (Gesellschaft, an organisation of like-minded people with shared goals).

The former was in danger of being closed to "outsiders" (such as "non-Aryan" Christians in the German Evangelical Church), and the latter lacked organic unity.

Bonhoeffer looked for a Church that transcended both these models. He called for a relationship between the Church and the world which "does not consist in a senseless hostility to culture", but in the "sanctification of all human life through the word of God and the Holy Spirit".

Bonhoeffer's second book, Act and Being, has been called "one of the great theological achievements of the 20th century". It explores how we can continue to talk about God without resorting to outdated metaphysics or pious platitudes. This time, the opposition that Bonhoeffer attempts to overcome is between German idealism in the Hegelian tradition, and phenomenology, as represented by Husserl and Heidegger.

The problem of the former is that it makes "God" the "object of its own system of thought", while the latter focuses on the experience of the subject, bracketing the question of the existence of any religious object. The solution, Bonhoeffer says, lies in revelation as understood and practised within the concreteness of the Church, which is "Christ existing as community".

These brilliant books would have given Bonhoeffer a key position in German theology had not the Third Reich intervened. Instead, at the beginning of his career as a lecturer in Berlin in January 1933, he was thrust into the forefront of the struggle against the Nazification of the German Evangelical Church.

HIS campaigning in the church elections that summer brought his first encounter with the Gestapo. Far more radical than other members of the Confessing Church, who seemed more intent on preserving their own doctrinal purity than opposing Hitler's plans for Germany as a whole, Bonhoeffer quickly saw the need to put a "spoke in the wheel" of government policy.

His primary concern at this stage was with the treatment of Jewish Christians - ethnic non-Aryans who had been baptised, but were threatened with exclusion from the national Church.

Charged with "incitement against the Fatherland", and warned against "high treason", Bonhoeffer fled to London, where he continued to help lead the rebellion against the church leadership, and forged a close friendship with Bishop Bell.

He also learnt, from one of his fellow-pastors of the Lutheran Church in England - encountered on a bus from Bradford to York - that, at times of crisis, it was better to write and speak more simply, in terms that ordinary people could understand.

He returned to Germany in 1935, at the request of the leadership of the Confessing Church, to take up the direction of a seminary at Finkenwalde, in the north-eastern corner of Germany, now Poland. Here, he saw himself as building a community of Christian pastors with the strength and discipline to resist persecution, and establish the new Germany that would follow the overthrow of Hitler.

BONHOEFFER's teaching during this time can be seen in what became a "devotional classic" when it was translated from the German Nachfolge, of 1937, into the English Cost of Discipleship, in 1948. Here he argues, in simpler terms than in his first two books, for a Christianity based upon "the pure word of Jesus", without all the "human ballast" of doctrine and regulation accumulated over the centuries.

He sets "costly grace" (obedience to the call to a life of service) against the "cheap grace" sold on the market as adherence to a set of propositions. Bonhoeffer inveighs against the "false Protestant ethic" that had diluted Christian love into a religion of hard work and patriotism. In the immediate context of Nazi Germany, to follow the teaching of the Sermon on the Mount meant resisting oppression and speaking up for the downtrodden.

The second of the "devotional classics" emerging from his time at Finkenwalde, and written in four weeks in 1938, after his seminary had been shut down, was Life Together. Christians, Bonhoeffer had come to realise, now lived like Christ "in the midst of enemies", and needed "the physical presence of other Christians" to survive.

They also needed the discipline of Bible reading, and the sacraments, especially confession and the Lord's Supper, to build up sufficient strength to resist the evils with which they were surrounded. "Only those who cry out for the Jews", as he said at this time, "may also sing Gregorian chant."

BY 1938, Bonhoeffer had grasped the extent of Nazi intentions towards the Jews and the need for political resistance. Exactly when he joined the group of about 50 people working to overthrow the Nazis from within military intelligence is unclear. But from late 1939 he was undergoing journeys for them, ostensibly gathering information for military intelligence but actually using his ecumenical connections to make the Allies aware of the activities and extent of the resistance.

From February 1941, after spending four months at the Benedictine monastery in Ettal, working on his Ethics and liaising with Roman Catholic as well as Protestant members of the resistance, he was officially appointed a "sub-agent" of the Abwehr in Munich.

He compiled reports - sent on to London by the World Council of Churches - of the deportation of Jews from Berlin at the end of 1941. He also played a small part in the smuggling of Jews into Switzerland later that year; visited Norway to encourage Lutheran resistance there in April 1942; and met Bishop Bell in Sweden that July, providing him with full details of resistance activity, in the forlorn hope that the British Government would work with them.

The Foreign Secretary, Anthony Eden, however, dismissed Bell as a "pestilent priest". And Churchill refused to believe in the existence of a German resistance unless it actually "did something".

BONHOEFFER was arrested in April 1943, and spent the remainder of his life in prison: first in the relative comfort of Tegel, where he was allowed access to books and writing material; but from October 1944 in the Gestapo cellar in Prinz-Albrechtstrasse. Finally, in February 1945, he was transferred to the camp at Buchenwald.

It was in Tegel that he produced his final fragmentary thoughts on the future of Christianity, the Letters and Papers from Prison which so excited Bishop John Robinson and the "Death of God" theologians in the 1960s.

These have to be read carefully, however, in the context of his prison reading. Those paradoxical phrases about "religionless Christianity" for a "world come of age", for example, are Bonhoeffer's response to Wilhelm Dilthey's account of the historical development of Christianity through a range of phases, from patristic and medieval metaphysics, through Protestant "inwardness", to scientific modernity.

We should not identify Christianity with any of these stages, Bonhoeffer argues; they are all historically contingent expressions of faith. In particular, we should abandon the "other-worldly" and individualistic interpretation of salvation in favour of a "this-worldly" realisation of God's Kingdom. "Christ takes hold of human beings in the midst of their lives," he says, while God is to be found not at the "boundaries" of the world - where science does not reach - but at its centre.

Bonhoeffer's reputation, carefully tended by his friend and biographer Eberhard Bethge, grew exponentially after the war, especially among Evangelicals in the United States, where there is something of a cult of this "hero of faith". There have been several novels and films of his life, the most recent available on DVD as Bonhoeffer: Agent of Faith, cashing in on the glamour of his life as prophet and spy (as well as lover).

There are organised pilgrimages to Pomerania and other key sites of importance in his personal journey. All these are part of what Stephen Haynes calls "the Bonhoeffer Phenomenon". But the starting point for a full appreciation of the courage and complexity of the man should be his own writings, now available in the newly completed 17 volumes of the Fortress edition of his works in English.

Terry Wright is Emeritus Professor of English Literature at Newcastle University. He is currently writing a novel about Dietrich Bonhoeffer.