What is the theme in Much Madness Is Divinest Sense by Emily Dickinson?

The main, or at least most obvious, theme of this poem deals with the argument over the definition of sanity and its opposite, madness. Sanity is an ambiguous term. It takes on its definition from its surroundings. What is considered sane in one society might be defined as crazy in another. The passage of time also alters the definition.