There are a couple of important reasons for citing your sources:
Academic texts should account for the author's own research results and arguments, but also position herself in relation to earlier research in the same or similar areas.
By referring to earlier research, the author can strengthen her own arguments and credibility. If you ignore doing this you will be subject to plagiarism.
In order for the reader to easily check the sources it is important to be accurate and consistent when citing the sources and writing the references. There are several different reference styles and which one to choose is usually decided by your teacher.