The literature review is a vital part of the argument the author makes in support of a thesis. The literature review offers brief descriptions, summaries, and critical evaluations of each work, and does so in the form of a well-organized essay. The goal is to summarize, synthesize, and critique arguments and ideas of others, and point to gaps in the current literature.
The literature review shows where your own research work is situated in the current research landscape. The literature review sets the stage for showing how your own work advances and expands upon the work done before, fills in knowledge gaps, or maybe - in some cases - disproves or debunks what was previously thought to be true. The literature review, therefore, is an essential part of a well-researched thesis, so it's important to do it right.