Rules are instructions that tell people what to do or what not to do. Good citizens always obey the rules.
School rules are important to follow because they enable the class to run smoothly so that everyone can learn and benefit from what the teacher has to offer. When students follow school rules, everyone, from the teachers to the students, can achieve their goals in the classroom.
If teachers didn't institute rules, and students didn't follow them, the classroom environment would be chaotic. They are instituted in the workplace, so students should learn to follow rules before they get to adulthood and need to abide by them to make a living.
Rules in the classroom typically pertain to following a teacher's instructions and respecting classmates. These types of policies are easily translated into the professional world, and respect and following instructions are valuable skills to learn.