Peter Leithart helpfully explores how the ancients did not consider metaphorical language to be a mere adornment of the literal, but rather as as essential tool to communicate reality. A snippet:
Allegory was certainly not mere adornment, a clever way of getting to something that could be expressed otherwise. Allegory’s primary setting in ancient thought is not in rhetoric but in philosophy. When we examine philosophical treatments of the subject, “we find that there is much more to be said about the subject than we might have been led to expect from the rhetoricians’ account, which makes allegory an ‘ornamental’ trope just like metaphor, of which it is listed as a species. For the philosophers might agree that allegory has an aesthetic appeal of its own; but they rarely argue that allegory is employed solely, or even mainly, for the sake of adornment. . . . the Platonist commentators on the ancient poets appear to have believed that allegory, far from adorning their meaning, was often the only means available for expressing what needed to be said” (3).