There is much to consider before formulating a thesis statement for Nathaniel Hawthorne's The Scarlet Letter. One valid reason is because there are so many viable themes and symbols running throughout the novel. For the purposes of answering your question, let us use theme as an example. The whole concept and interpretation of sin, revenge, fate versus free will, guilt and hypocrisy, and judgment are all good workable themes with which to develop your thesis. Your thesis, of course, depends on what exactly your instructor is asking you to contemplate and critique.
For an example, let us choose judgment as a theme with which to work on a strong thesis statement. The Scarlet Letter takes place in a very strong religious environment known as Puritanism. This was a very strict religious code that many lived by during this period in American history. Generally speaking, whenever there is a very strict religious way of life, there comes with it a plentitude of judgment, whether justifiable or not. That is what you might want to think about as you form a thesis statement. For instance, Hester Prynne is the victim of societal judgment to an extreme degree. After all, Hester is forced to wear a scarlet "A" as a symbol of her adultery. Then, she is paraded through the streets for others to judge her sin. What's worse is that suddenly her husband appears ready to seek revenge. The amount of judgment she is forced to endure is almost unfathomable, especially if you consider her supposed sin from a gender point of view. Are the rules the same for men as for women during this historical period? Why or why not? People love to judge and formulate punishments based upon those judgments. Your thesis could go in several directions, but the strongest thesis is one that focuses on a particular aspect.
Here is an example you may want to think about. Make sure, as with any thesis statement, that you feel comfortable backing up your statement with both textual proof as well as formal critique. SAMPLE THESIS: In Nathaniel Hawthorne's The Scarlet Letter, Hester Prynne suffers unjust punishment at the hands of the townsfolk, her husband, and the rules of the Puritan religion. Within the thesis example above, the writer states his/her argument as to what the essay is going to be about, and what exact direction the paper will take in relation to the theme. If you happen to be writing a typical five paragraph essay, you will provide your thesis in the introductory paragraph. Then, using the hypothetical three body paragraph ideas from the above thesis, judgment from society, her husband, and her religion, this is how you would construct the following body paragraphs. Remember that this example is written for a typical five paragraph essay. You may need to tailor it spcifically depending upon what the instructor is asking. You can always add more or less body paragraphs depending on the required assignment.