I believe the answer is: William the Conqueror took control of most of England's lands and, eventually, a set of common laws was established for all Englishmen.
Laws would force people to a certain standard, regarding the things that they are allowed and not allowed to do within the society. He saw establishing common laws for all englishmen would establish a similar set of principles among his people and very important in developing one national identiy that separate them from other civilizations at that time.