What is the theme of William Faulkner's "Snopes?"?

I ume you are referring to the Snopes' trilogy and not to any one book amongst them? If that's the case - Evil and corruption are the primary themes of the Snopes' trilogy. Love is another of the themes and, with it, Faulkner presents a counterbalance to the negativity of the other two themes and introduces a semblance of hope and optimism into these three books.