Cicero, Institutio Oratoria, Book II, VIII, 3.
For it is a better exercise for the memory to learn the words of others than it is to learn one's own, and those who have practised this far harder task will find no difficulty in committing to memory their own compositions with which they are already familiar.
Further, they will form an intimate acquaintance with the best writings, will carry their models with them and unconsciously reproduce the style of the speech which has been impressed upon the memory. They will have a plentiful and choice vocabulary and a command of artistic structure and a supply of figures which will not have to be hunted for, but will offer themselves spontaneously from the treasure-house, if I may so call it, in which they are stored.
In addition, they will be in the agreeable position of being able to quote the happy sayings of the various authors, a power which they will find most useful in the courts. For phrases which have not been coined merely to suit the circumstances of the lawsuit of the moment carry greater weight and often win greater praise than if they were our own.