My initial thoughts about this distinction is that it centers around the role of rhetoric in language, and its relation to philosophy, or philosophical language. Typically, rhetoric is considered as the speech that acts on the emotions. This is what preachers, politicians are adroit at in order to manipulate emotions, and they develop a technique of persuasion.
Is philosophy rhetorical? If we predetermine philosophy as a rational process or theoretical thinking, a theoretical mode of thinking or speaking or writing, then it does not include rhetorical elements, for “emotions” are incongruent with the nature of rational thought. The old school philosophers like Kant disparage rhetoric as something that deludes and borrows from poetry just enough to win over people before they think about the subject.
However, perhaps the old school philosophers have been too hasty in their attempts to condemn rhetoric, for it may already possess a philosophical structure.
In order to claim to know something, one must be able to prove it. To prove is to show something to be something. And in order to do that is to use demonstrative speech, which establishes the definition of something by tracing it back to first principles. Now, these first principles themselves cannot be proved or be the object of demonstrative speech. Were it otherwise, they would not be the first principles. They are non-deducible. If these original principles cannot be demonstrable, then they cannot be characterized as rational or theoretical.
If the first principles themselves are non-deducible then they do not have an apodictic or demonstrative character. They are instead “indicative” or allusive, and that gives the rational speech the framework in order to function. Because rational speech is the process of clarification, then the original clarity of the first principles are not rational, for they “show.” Something that shows is figurative or imaginative, metaphorical, showing something that has a sense. The first principle is a speech that transfers a sense. Thus, indicative speech is structurally imaginative. We consider metaphor as the fundamental character of rhetorical speech, then all original or “archaic” speech are not rational but rhetorical speech. In other words, rhetoric is not just the art of persuasion, it is the speech that is fundamental for all rational language. Rhetoric comes before rational language.
We use original speech to indicate sense in first-hand experience, and that means the essence of speech is semantic: immediate, not deductive or demonstrative, illuminating and purely indicative. Rational language is dialectical, mediating and demonstrative, and lacks any pathetic character whatsoever. Original speech is fundamentally figurative, metaphorical, and ultimately, a pathetic essence.
Formally, the language of the sacred and religious world is original, immediate, and purely semantic, whereas the language of the rational and historical world is mediating, demonstrating, and apodictic.