Dietrich Bonhoeffer (1906–1945) is a famous German theologian, member of German Resistance movement, who died in a Nazi concentration camp. In his theological letters to his friend and pastor Eberhard Bethge emerges his theological concept of “non-religious Christianity”. Formulated only in sketches in personal letters to his best friend, the concept became a significant contribution to the development of Western theology of the 20th century. The article reveals the significance of the researched concept as an appeal to the church based on the ministry of the Christian Church in the modern world, which has become nonreligious. The content of the concept is revealed in a number of theses formulated in the theological letters. Firstly, religiousness is defined as an individual and metaphysical understanding of Christian life. Secondly it is claimed that believers recognize the transcendence of God through fellowship. Thirdly, according to Bonhoeffer, the modern world has become mature (adult) and has learned to answer the most complex questions without resorting to God. Therefore, the church must learn to live in a non-religious world in the image of a serving community. This requires a revival of catechesis, that is, the consistent entry of new members into the mysterious and dogmatic teachings of the Church, on the one hand, and the external openness of the Christian community to the testimony of Christ, on the other.
Keywords: Christian community, epistolary, German theology, Resistance movement, non-religious Christianity, Bonhoeffer.