The general purpose of literature review is to narrow down the focus of your research, to focus on it, and to help readers relate it to your research. Purposes of a literature review includes:

To identify the field and specific context in which the topic is located.
To decide which research and methodology will be adopted, which type of data may be collected and analyzed.
To deepen your knowledge related to the key concepts of the research topic
To avoid repeating previous studies that have ben completed before your attempt and to produce an original work.
To avoid the mistakes that past studies reported.
To discover the key people, organizations, and papers related to your research topic.