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.
In practical matters the end is not mere speculative knowledge of what is to be done, but rather the doing of it. It is not enough to know about Virtue, then, but we must endeavor to possess it, and to use it, or to take any other steps that may make.