The Introduction discusses the reasons for writing this book. Given the range and magnitude of Niebuhr's corpus, it states, any commentary on him can only provide a partial view, and any attempt to summarize his thought will be incomplete. This isn't helped by the fact that Niebuhr's writings are well-known for being unsystematic. However, this text argues that there was a discernible vision animating through his writings. Niebuhr's theological approach remains divisive today. Leading thinkers have many different opinions on Niebuhr's effort to exercise responsibility in the present age. The Introduction ends by outlining how the book develops a holistic picture of Niebuhr's theological vision and how he applied it to the historical events of his time.