The original expression is, "May the force be with you." Then the fan holiday of May 4th came about because it sounds similar when you say, "May the fourth be with you." Over time as with lots of things individuals come up with corporations have gotten involved and now May 4th is basically the biggest official holiday for fans of the Star Wars franchise. I have enjoyed the Star Wars-related stuff I have seen but am by no means an expert. It is cool to have a Star Wars-related day though!