Quintilian, Institutio Oratoria, Vol. IV (Loeb)

...picture, but by bringing us into actual touch with the things themselves. Then all is life and movement, and we receive the new-born offspring of his imagination with enthusiastic approval. We are moved not merely by the actual issue of the trial, but by all that the orator himself has at stake.

17 Moreover, his voice, the grace of his gestures, the adaptation of his delivery (which is of supreme importance in oratory), and, in a word, all his excellences in combination, have their educative effect. In reading, on the other hand, the critical faculty is a surer guide, inasmuch as the listener’s judgment is often swept away by his preference for a particular speaker, or by the applause of an enthusiastic audience.

18 For we are ashamed to disagree with them, and an unconscious modesty prevents us from ranking our own opinion above theirs, though all the time the taste of the majority is vicious, and the claque a group of people hired to applaud may praise even what does not really deserve approval.

19 On the other hand, it will sometimes also happen that an audience whose taste is bad will fail to award the praise which is due to the most admirable utterances. Reading, however, is free, and does not hurry past us with the speed of oral delivery; we can re-read a passage again and again if we are in doubt about it or wish to fix it in the memory. We must return to what we have read and reconsider it with care, while, just as we do not swallow our food till we have chewed it and reduced it almost to a state of liquefaction to assist the process of digestion, so what we read must not be committed to the memory for subsequent imitation while it is still in a crude state, but must be softened and, if I may use the phrase, reduced to a pulp by frequent re-perusal.