Development
The essay's thesis is the main point you are trying to make, using the best evidence you can marshal. Your thesis will evolve during the course of writing drafts, but everything that happens in your essay is directed toward establishing its validity. A given assignment may not tell you that you need to come up with a thesis and defend it, but these are the unspoken requirements of any scholarly paper.
Deciding upon a thesis can generate considerable anxiety. Students may think, "How can I have a new idea about a subject scholars have spent their whole lives exploring? I just read a few books in the last few days, and now I'm supposed to be an expert?" But you can be original on different scales. We can't possibly know everything that has been, or is being, thought or written by everyone in the world—even given the vastness and speed of the Internet. What is required is a rigorous, good faith effort to establish originality, given the demands of the assignment and the discipline. It is a good exercise throughout the writing process to stop periodically and reformulate your thesis as succinctly as possible so someone in another field could understand its meaning as well as its importance. A thesis can be relatively complex, but you should be able to distill its essence. This does not mean you have to give the game away right from the start. Guided by a clear understanding of the point you wish to argue, you can spark your reader's curiosity by first asking questions—the very questions that may have guided you in your research—and carefully building a case for the validity of your idea. Or you can start with a provocative observation, inviting your audience to follow your own path of discovery.