Oscar Wilde's preface to The Picture of Dorian Gray consists of a list of Wilde's aphorisms that deal directly with art, artists, critics, and audience but only obliquely with the novel. They speak to the importance of beauty espoused by the Aesthetic movement.
The preface offers one of Wilde's most famous aphorisms: "There is no such thing as a moral or an immoral book. Books are well written, or badly written. That is all." According to Wilde, the artist might consider the moral or immoral lives of people as part of the subject matter of a work, but art itself is not meant to instruct the reader. The true artist is not out to prove anything and makes no judgments of right or wrong. What people call "vices" or "virtues" are merely materials for the artist. Those who attempt to go beneath the surface of a work, or to read meaning into a symbol, do so at their own risk. Considerable disagreement about a work of art only proves that the work is "new, complex, and vital."
Wilde concludes the preface by saying that it is fine to create something useful so long as it is not admired as art. The only reason for creating something useless is to admire it a great deal. Thus, "All art is quite useless." That is, it exists for its own sake as art ("art for art's sake") and not for some moral purpose.
The preface sets the tone for the book and lets the reader know that The Picture of Dorian Gray will be a book of expansive ideas and wonderful language.