The author must have people read his work before it is considered finished. I discussed editing in my previous post.
Readers are a vital part of the editing process. They will spot almost all of the grammatical errors that the author could not see. They will also suggest story improvements that the author can make. But when the author tackles these corrections, he will create more errors. It is too much to ask readers to read minor edits. Perhaps if the author has changed a significant part of the work, the reader would not mind reading the new sections.
Finding good readers is not necessarily easy. A good reader has to appreciate the kind of story that the author writes. People who do not like fantasy will probably make bad readers of fantasy. If the author has a priest pull someone back from the Spirit World on page 1, the non-fantasy reader will likely assume that the priest is a Catholic priest to whom the Christian God granted a miracle. The reader will be confused when the priest turns out to wear armor and wield a sword. The reader's frustrations will boil when the priest tells his wife (priests can have wives????) that his God is angry that the priest snatched someone from His realm (why did his God let the priest do it if it would make Him angry???).
A good reader not only needs to appreciate the genre, but needs to be able to appreciate the author's writing style. If the reader expects to see the story begin, "Jared, the God who guards the Spirit Door, gives powers to his armored warrior priests," he will be confused by a writer who tends to convey information through scenes with characters, setting, action, and dialogue.
A good reader will be honest with the author and not just say, "I liked it," if he did not.
A good (skilled) reader can be specific about the things that were wrong with the story. The good reader will be able to say, "I was bored because I knew that the hero was not going to fail. I knew the hero was not going to fail because she never worked hard to solve her problems."
A good reader does not mind being debriefed by the author. What does it mean to debrief a reader? More on that later.