Stories that endure are those that speak to people of truth. Moral stories tell of a good man who goes from rags to riches or good people who triumph over evil for the betterment of themselves, family, friends and society.
Dickens stories are a perfect example. http://en.wikipedia.org/wiki/Charles_Dickens
The purpose of your story may be only to put a few dollars in your pocket, but writing provides an opportunity to make the world a better place.
Eventually every writer has a legacy, what’s yours?