Literary criticism can be really helpful. I've had lots of opportunities to praise some article or book this year for explaining a theme of Renaissance revenge tragedies that I would never in an epoch have figured out on my own. But without exception, the best literary criticism is written by those who are tea-bag-steeped in the literature they are writing about, and ideally, in all the literature that precedes the literature they are writing about. Psychoanalysis, Marxist theory, whatever it is that Foucault is talking about — these things have their place, but at the end of the day, literature is about literature.
In the preface to The English Poetic Mind, Charles Williams agrees:
Criticism has done much to illuminate the poets, and yet it seems, with few exceptions, still not sufficiently to relate the poets to the poets, to explain poetry by poetry. Yet in the end what other criterion have we? Wordsworth's poetry is likely to explain Shakespeare's poetry much better than we can, because poetry is a thing sui generis. It explains itself by existing.
Anne Ridler explains how this worked for Williams in her introduction to the essay collection Image of the City:
When he comes to consider Dante's exclusion of Virgil from Paradise, [Williams] is not hampered by the usual irrelevant emotional considerations, but points out that the poem could not afford to keep him in. 'The Aeneid has pietas and not caritas; so must its author have here.' So also, when Williams comes to consider the idea of chastity in Milton, he sees it as the poetry presents it, without the least clouding of our modern cant about this virtue.
On that last point, in my class on Renaissance revenge tragedy, we spent several minutes debating whether a female protagonist's comparison of her chastity to a "crystal tower" was an example of (dun dun dunnnn) patriarchy. Because, you see, towers are just so phallic, and so she's implying that her virtue is connected to masculine power or something. The whole conversation was utterly tone-deaf about the ways chastity has been portrayed in literature and poetry for literally thousands of years. It's always a tower, a fortress, a well-guarded keep. Of course, even if they'd known the history, some of my classmates might have come to the same conclusion about the crystal tower, but at least we would have been cutting with the grain of the literary tradition instead of against it.
This principle of interpretation also makes me think of the way Jim Jordan interprets the Bible. Scholar A will arrive at a tough passage in Daniel and say, "I better read up on ancient near eastern economic theory to explain these verses." Scholar B will arrive at the same passage and say, "These verses were clearly added later on by a scribe who wasn't quite as clever as he thought." Jim Jordan reads the passage and says, "You know, I remember reading something similar back in Exodus. Let's see if that helps illuminate it." And lo! It always does. Scripture, like lesser poetry, explains itself by existing.