The two ways of being at home in something is either to remain in that place from the beginning, or to go wholly around it and enter back into it from the outside with fresh eyes. Chesterton wants to take the reader on this second path, to see the entity of the Christian church with new eyes and against the backdrop of the whole of history and the enigma of the human person.

Judging the claims of the Christian faith must be done objectively and with clarity, and not by listening to a tired and apathetic critic who is often an “ill-educated Christian turning gradually into the ill-tempered agnostic” (5). The book will be divided into two principal parts: a study of the history of humanity, and a study of the change which Christianity made to history. The author is convinced that this “detached consideration of the curious career of man will lead back to, and not away from, the ancient faith in the dark designs of God” (18), and yet even if this does not occur, the exercise will have been worthwhile for the simple fact of having seen the question put up against the whole backdrop of humanity.