"Simul et jucunda et idonea dicere vitae."
(Horace, Art of Poetry)
"To teach - to please - comprise the poet's views,
Or else at once to profit and amuse."
"Two objects always should the poet move,
Or one or both, - to please or to improve."
(Byron's translation, in Hints from Horace)
"ut pictora poesis"
"in poetry as in painting"