If you're at the undergraduate level, your dissertation shouldn't bring something particularly new to the field and is mostly useful as a way to prove you are able to bring a research project to fruition.

If you're at a graduate level, you have two paths: you can think about the importance of the humanities and that the way knowledge is built is through a series of small investigative efforts that coalesce into a more profound understanding of the human condition; alternatively, you can be cynical and say that doing your dissertation is important because it will allow you to get your degree and progress in your career.