There are so many elements of writing that must work together for a story to be at its best. That being said, for me, the essential part of bringing a story to life is character development. Showing the human condition--love, hate, joy, sorry, struggles, triumphs, etc.--this is the common thread that binds us together, no matter where we come from or what we believe. It's why stories can change the way we perceive the world--it's just that powerful.