I'm writing an essay on the scarlet letter, need thesis help.?

Well, you just start off with a good arguable thesis. Maybe something like: "In Nathaniel Hawthorne's "The Scarlett Letter", the motif of darkness and light functions to highlight the conscience at work in the character of Chilingsworth". Then think of three instances where the story supports that idea and write a paragraph for each. Just examine what the motif does for you when you read the story. What does it draw attention to or emphasize or make you contemplate upon?