At the risk of sounding like a broken record, we all know that writers need to be voracious readers. Most of us write stories because we enjoy reading them. However, as writers we also need to read widely to be able to recognize what works and what doesn't, what genre conventions are accepted, etc. So, the question then is what should you read? While I think that you should certainly read widely within your chosen genre or field of interest, I also think that everyone can benefit from reading the classics, the literary canon.
Of course, there is no official literary canon. No one regulates what we consider to be part of the canon of classic literature, but a simple Google search will reveal what kinds of books and authors are included in this canon. In general, classic literature is largely written by white men and has much less representation of women and people of color. So, is it still relevant? Writing styles change, fads come and go, and society (hopefully) progresses forward. So, should we continue to read the likes of Shakespeare or Dickens? Absolutely and I'll explain why.
Retellings and Derivative Works
If you've ever watched Clueless or Ten Things I Hate About You, you've watched an adaptation of a literary classic. Clueless takes Jane Austen's Emma and sets it in Beverly Hills, with Cher as the hapless matchmaker. 10 Things I Hate About You updates the Shakespearean classic The Taming of the Shrew for a '90s audience. There are plenty of books and movies that are direct retellings of classic stories. As long as the stories are out of copyright and in the public domain, you are free to remix and retell them however you choose. When done well, retellings don't just plunk the story down into a different time or place, but adjust the themes and viewpoints to resonate with a new audience.
Classic Story Structures
When reading classic literature, I often find that the story's structure or general plot can feel very familiar to me. Even when writers don't retell a story in its entirety, many writers pull from well-known story arcs. For example, Kurt Sutter's outlaw biker drama Sons of Anarchy pulls heavily from the themes and story structure of Hamlet in its early seasons. The plot of the show doesn't follow the play closely enough to be considered a retelling, but the dramatic family tensions between stepfather and son and the desire for revenge is something that connects the two works. Likewise, the enemies-to-lovers trope so common in romantic comedies today can be found in works like Jane Austen's Pride and Prejudice and even earlier in Shakespeare's Much Ado About Nothing. No one can write in isolation from the work that came before them. These stories have plots that are enduring because they connect with us on a deeper level.
Know Your History
Beyond just what you can mine from the classics for use in your own writing is the fact that these works are part of our literary history. Even if you don't reference the characters or plot of Dracula, it is impossible to write a book on vampires without being in some way influenced by that original story. Though you may never have read Romeo and Juliet, the idea of star-crossed lovers has so permeated our culture that you immediately recognize it. Reading classic literature, having a sense of the canon that has helped to form our culture, can help you to better understand the foundations on which you seek to build your own stories.
Learn from the Masters
To state the obvious, there is a reason that the classics have endured: they're good. If you struggle to write compelling description, look no further than Charles Dickens as an example of how to lay out a scene. Dickens wrote his works in a serialized form, therefore the longer he could draw out a story, the more he would get paid. The result was books that were full of detailed descriptions of just about everything. There is much to be learned from classic literature. Though writing styles change and tropes fall out of fashion, these works remain masterpieces.
There is a reason that artists still study the Old Masters. I think the painter Sir Joshua Reynolds can best sum up why we need to study the greats who came before us: "Invention, strictly speaking, is little more than a new combination of those images which have been previously gathered and deposited into memory: nothing can come of nothing: he who has laid up no materials, can produce no combinations." Fellow writers, gather your materials.