The purpose of reading a short story is the same as for a long story: to learn, to be entertained or enlightened, and to simply appreciate a work of literature for its own sake. Short stories are just that: short stories. Not every idea lends itself to a full-length novel, and many writers of novels, for example, Frederick Forsyth, enjoy penning the occasional short story or publishing a collection of short stories as an alternative to a single story told over 300 pages.
Just as many authors enjoy the opportunity to write short stories, many readers enjoy the limited scope of short stories, which can extend anywhere from two to 80 or 90 pages. Short stories provide authors the freedom to convey a message or experiment with a theme without the burden of committing to a lengthier, more time-consuming task. By their nature, they are more accessible to more categories of readers, especially students, and provide a more concise format than full-length novels. Short stories like Flannery O'Connor's "Good Christian People," Shirley Jackson's "The Lottery," Edgar Allan Poe's "The Fall of the House of Usher," and O. Henry's "The Gift of the Magi" continue to be widely read precisely because of their value as works of art. A lot can be written in a few pages that conveys as much meaning as messages delivered over the course of hundreds of pages. One form is not superior to the other. It is entirely dependent upon the form in which the author has chosen to tell his or her story.