Here's a novel idea: literary works are about exactly what they seem to be about. Wallace Stevens's poetry is about the relation between the poetic imagination and reality. Ezra Pound's work is about economics and his own particular view of history. Honor plays are about honor. Homer is about Homeric heroes and their code of behavior. Unamuno's
Abel Sánchez is about its announced and ostensible theme: envy. "Howl" is about how the best minds of his generation have been destroyed by madness, starving hysterical naked. If I have read any poem or novel I know what it is about.
To the extent that you understand what the action of a narrative is, the plain sense of the words of a poem, you understand the literary work itself. Sure, you can talk about some themes that aren't explicitly enumerated, but that's simply a way of abstracting concepts from concrete situations. For example, in a play about two brothers fighting for succession to dynastic power, we could talk about the "theme of legitimacy." The big abstract thematic words like power, alienation, love, death, envy, are never at too far a remove from what the play or poem is actually dealing with right on the surface. There's difference between saying "It's a play about a guy who can't find a job" and "It's an examination of the limitations of the American dream." The latter sounds more sophisticated because it is more abstract.
Writers do not write in secret code. The meaning of their works is not concealed beneath the surface. If it were, then would they expect nobody to understand them until some clever dude cracks to code 300 years later? That doesn't seem very plausible. Usually, the meaning of the text is in plain sight. The clever dude with his esoteric theory is always wrong, because nobody
encodes a message that deep into the text. That's just not the way literature works because it just wouldn't be viable that way.
Allegorical works
Pilgrim's Progress like Dante's
Commedia point us directly in the direction of their allegory. There's no mystery to what they are about.
Metaphors in poetry are very conventional. Life is a road. A human being is a tree. The night is something negative, something to be surpassed. Morning is hope. The sun is a powerful source of heat and life. 90% of poetic metaphors are of this type.
All this being said, many people are terrible readers. I would suggest that they are terrible because they are looking for a secret code and forget to look at what the text is saying on its face. This is especially true of difficult texts. If you understand a difficult text on its face, what the words are actually saying, you won't even need to find an esoteric meaning. If there is an esoteric system, it will be available, more or less, in the writer's complete works, as in the case of William Blake.
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My entire profession, nevertheless, exists because things are not quite as simple as I've laid out here. They are a little more complicated and nuanced, and this little bit has made all the difference.