Against Interpretation" Susan Sontag exposes Plato's mimetic theory in one paragraph in a very simple way:
"t is at this point that the peculiar question of the value of art arose. For the mimetic theory, by its very terms, challenges art to justify itself.
Plato, who proposed the theory, seems to have done so in order to rule that the value of art is dubious. Since he considered ordinary material things as themselves mimetic objects, imitations of transcendent forms or structures, even the best painting of a bed would be only an "imitation of an imitation." For Plato, art is neither particularly useful (the painting of a bed is no good to sleep on), nor, in the strict sense, true. And Aristotle's arguments in defense of art do not really challenge Plato's view that all art is an elaborate trompe l'oeil, and therefore a lie. But he does dispute Plato's idea that art
is useless. Lie or no, art has a certain value according to Aristotle because it is a form of therapy. Art is useful, after all, Aristotle counters, medicinally useful in that it arouses and purges dangerous emotions.
In Plato and Aristotle, the mimetic theory of art goes hand in hand with the assumption that art is always figurative. But advocates of the mimetic theory need not close their eyes to decorative and abstract art. The fallacy that art is necessarily a "realism" can be modified or scrapped without ever moving outside the problems delimited by the mimetic theory."
I hope it helps. Sontag's book "Against Interpretation" highlight the intrinsic values of art that doesn't need other discourses to be explained.