There is the class of history books and the class of forensic books, that is to say, the books of facts and the books of argument. No one would wish to belittle either kind. But when we think of a book proper, in the sense that a Bible means a book, we mean more than this. We mean, that is to say, a revelation of something that had remained latent, unconscious, perhaps even more or less intentionally repressed, within the writer's own soul, which is, ultimately, the soul of mankind. These books are apt to repel; nothing, indeed, is so likely to shock us at first as the manifest revelation of ourselves. Therefore, such books may have to knock again and again at the closed door of our hearts. "Who is there?" we carelessly cry, and we cannot open the door; we bid the importunate stranger, whatever he may be, to go away; until, as in the apologue of the Persian mystic, at last we seem to hear the voice outside saying: "It is thyself."

Havelock Ellis, from The Dance of Life (1923)