Have you ever noticed how when we read a story, the events always happen in the same sequence? We are teaching our children about how to tell a story by the predictability of the events. For example, the bluebird song in "Animal Serenade" is always first - and the mouse page always has us "peeping" through our fingers. It's important to the reader or listener to have events told in a cohesive, and logical way so that the story is fully understood.
Additionally, telling a story to your children in a predictable way now, will help them develop essay skills when they are older. And using your hands to tell a story to a young child, helps engage them with another sensation, increasing their attention and retention.