As a writer, you must concern yourself with the reader’s experience. When you craft a scene in which a character is grieving the death of a beloved dog, you want the reader to feel that particular sadness and loss. When you end a chapter with a compelling dramatic question, you want the reader to feel that pressing urge to turn the page to find the answer. Reading widely gives you direct personal experience as a reader. You engage with the story—and all the craft components within it—and make observations about what works and what doesn’t. You can assess different approaches and styles. That direct experience as a reader can help inform the choices in your own writing.
In On Writing, Stephen King writes, “If you don't have time to read, you don't have the time (or the tools) to write. Simple as that.” Reading allows you to witness the possibilities of the craft. As you read, you accumulate knowledge about what has been done and how it has been done. You gain an understanding of the diverse approaches to the craft and the effects of those choices on the reading experience. All of this observation sharpens your writerly and editorial eye, which is useful when you turn it back to your own work.
Some of this knowledge can be gained in a conscious way. Ask yourself craft-based questions about the work: Why did the writer choose that particular point of view strategy? How does the setting heighten, accentuate, or otherwise interact with the character’s conflict? How is the end a resolution to the action that has come before? Carefully deliberate elements that stand out to you. You may find, too, that some of the knowledge is internalized. Consistently reading may allow you to more intuitively understand important qualities of fiction, such as the rhythm or movement of a strong story arc or the point at which you’ve sufficiently developed character.