Here's St Augustine:
(On Christian Teaching.)
(You could say much more about this quote. For example, Augustine also thought that a 'helpful and healthy obscurity' was a characteristic of the scriptures, and shouldn't be a characteristic of Christian teachers; those questions could be argued; but leave that aside for a moment, or imagine he is just talking about parables.)
Boccaccio in his Life of Dante (1374) made a similar remark about poetry:
Both these quotations are lifted directly from the discussion on storytelling in Jules Lubbock's art history book, Storytelling in Christian Art from Giotto to Donatello.