Rules are extremely important to any game. According to different definitions of game mechanics, they might not be defined as mechanics themselves, but as a part of them. Rules for our combat system could be, for example, the number of attacks per second the player can perform. Rules can define constraints for actions or conditions to be respected (a victory condition, for example). Rules make games exciting because they determine the space in which the game's actions can take place.
Imagine a Hide and Seek game where the seeker doesn't have to close his eyes while the other players are hiding. That would be the most boring Hide and Seek game ever! The rule that states the seeker has to close their eyes and count ...
