Societies should have rules and laws so that everyone can have a basic understanding of legal right and wrong. This way people know where the line is drawn on their actions. The difference between rules and laws, are that while rules may be dictated on solely social means, laws are held to a legal standard with legal punishments for breaking them.
A rule can become a law in a society if the society can agree that it would be dangerous and harmful to the society if that rule were to be broken.
The rule of law is a principle that a nation has standard laws that it rules on, rather than attributing crimes to whatever the leaders find punishable on their own whim. A society without rule of law could mean citizens don't know what is legally okay to do, and they might not understand the severity of their actions since they may be subject to change.
Rule of law affects government leaders since the laws are made public to the people, instead of just opinions carried out by those same leaders. This means that leaders can be held to the same standard of law and can have watchful eyes from their people. This is why transparency plays a big role in rule of law, since citizens may find it unfair if government leaders are held to different standards or no standards at all.
