An author in his book must be like God in the universe, present everywhere and visible nowhere.

Gustave Flaubert (1821–1880) French writer, novelist

Letter to Louise Colet (9 Dec 1852)
    (Source)

In a later letter to Leoroyer de Chanepie (18 Mar 1857), he repeated the sentiment: "The artist must be in his work as God is in creation, invisible and all-powerful; one must sense him everywhere but never see him."