What is the theme in A Treatise of Human Nature by David Hume?

Anatomy is another important theme in the book. The most common interpretation of The Treatise is that Hume is making substantive arguments that one should think of the understanding thus-and-so, or of passions in a particular way, or of morality as he sees it. They see his account of the human being as primarily prescriptive; he is telling us what we should believe about his subject matter and major questions. However, some deny this and maintain that Hume is merely an 'anatomist' meaning that his primary aim is merely to give a philosophical and scientific account of human cognition, psychology, emotions, and morality.