While you read, you make the writer of the book you're reading happy. He or she wrote the book to be read, when you do so, you're making it all worthwhile for them. You contribute back to humanity by enjoying and using the work of others.

And if the book's purpose was to teach, and it delivered that promise, then by reading it, and gaining knowledge, you will 'perform' (lacking a better word off the top of my head) better, and will be more useful in the long run.

Reading is an investment. Read good books, and the investment will be worth it.