Rhetoric completes the tools of learning. Dialectic zeros in on the logic of things, of particular systems of thought or subjects. Rhetoric takes the next grand step and brings all these subjects together into one whole.
Really, the fundamental, ultimate mystery -- the only thing you need to know to understand the deepest metaphysical secrets -- is this: that for every outside there is an inside and for every inside there is an outside, and although they are different, they go together.
I am the entire human race compacted together. I have found that there is no ingredient of the race which I do not possess in either a small way or a large way.