Your readers need to know the sources you cited for the following reasons:
Why you need to give the credit to the authors who created the sources you used.
This is about ethical use of information. In addition, citing quality sources demonstrates your understanding of the research topic and giving the readers insight on how the topic has been studied in the past. The quality of the sources you cite also give credence to the quality of your study.
Why do I have to cite my sources in a specific style?
A style helps readers to identify and find the sources an author used. For example, you cite book chapters and journal articles differently. By reading your citation, readers of your article know immediately what kinds of information you cited.
Why are there so many different styles?
Different disciplines create different citation styles to accommodate a disciplinary tradition of scholarly communication. For example, in the sciences and social sciences, many use the Author-Date system.