What is the reationship between literature and rhetoric?
Comparing literature and rhetoric is rather like comparing animals and biological theories.
The term literature refers to imaginative works in specific genres including poetry, drama, fiction and literary essays or creative non-fiction. The tools normally used to analyse literature are called "literary criticism," which consists of a body of theories about literature. Examples are Aristotle's Poetics, Horace's Art of Poetry, and Dante's De vulgari eloquentia.
Rhetoric, like literary criticism, is a set of methods or theories, embodied in manuals and textbooks such as Aristotle's Rhetoric, Cicero's de Inventione, or Whately's Elements of Rhetoric. The main corpus of works to which rhetoric is applied is "oratory", i.e. public speaking, although the methods of rhetorical criticism, originally developed to analyse oratory, can be applied to literary texts just as the methods of literary criticism can be applied to speeches.