The purpose of this step is to evaluate your own work.
Your professor assigns you a research paper because they want you to learn about a topic, but also because they want you to learn how to think. Research papers and projects not only teach you how to find a good answer to a question when you are out in the real world, they also teach you how to weigh conflicting evidence, organize your thoughts, and combine personal experience, world view, and evidence in a way that allows you to be proud of and believe in your own answer. For this reason, reflection on the process is a key component to actually learning about how to write a research paper.