One way to think about references and how they contribute to any book or article is to envision an iceberg. When you see an image of an iceberg, often you only see the top of it which is 1/8th of the entire iceberg. The rest, the other 7/8ths, is located underneath.
In other words, references are the great, hulking part of the iceberg that float underneath. They point to all of the research--both primary and secondary sources that the author consulted. The sources serve as evidence for the author's argument. They also situate the author's argument in within specific academic conversations on a topic.