BOOK X. 1. 3-6

...which a thing is essential does not necessarily make it of immediate and supreme importance for the formation of the ideal orator. For obviously, the power of speech is the first essential, since therein lies the primary task of the orator, and it is obvious that it was with this that the art of oratory began, and that the power of imitation comes next, and third and last, diligent practice in writing.
4 But as perfection cannot be attained without starting at the very beginning, the points which come first in time will, as our training proceeds, become of quite trivial importance. Now we have reached a stage in our inquiry where we are no longer considering the preliminary training of our orator; for I think the instructions already given should suffice for that; they are in any case as good as I could make them. Our present task is to consider how our athlete, who has learned all the technique of his art from his trainer, is to be prepared by actual practice for the contests in which he will have to engage. Consequently, we must assume that our student has learned how to conceive and dispose his subject matter and understands how to choose and arrange his words, and must proceed to instruct him how to make the best and readiest use of the knowledge which he has acquired.
There can then be no doubt that he must accumulate
5 a certain store of resources, to be employed whenever they may be required. The resources of which I speak consist in a copious supply of words
6 and matter. But while the matter is necessarily either peculiar to the individual case, or at best common to only a few, words must be acquired to suit all and every case.