It was Augustine's habit to think during the day about the sermon he was going to preach the following day. Perhaps he even made it the subject of his meditation the night before. But when it came time for him to speak, with no notes, no prepared text, as was the custom of the time, he delivered it ex tempore. In the body of some sermons he even admitted that he'd tossed away his first thoughts in favor of an idea from the Gospel just read aloud to the congregation. Needless to say, because he always preached on materials that where dear to his heart, he was never at a lost for words.

"Just as in well equipped houses one need not go downstairs to fetch water but has it up there on tap, under pressure--one merely turns on the faucet-so also is that person an authentic Christian speaker who, because the essentially Christian is his life, at every moment has eloquence present, immediately available, precisely the true eloquence."
-Kierkegaard

-William Griffin in his new book, "Augustine of Hippo: Sermons to the People.