Power
Every day, you shout at a roomful of people to "rise"...and they do it. That's power, my friend. Well, it's power enforced by a vast system of power relations that has less to do with you than centuries of legal justice tradition. But still. You get to confiscate cell phones, make people swear to tell the truth, and tackle out-of-line defendants if they try something. Basically, you have the same power that a teacher or a volunteer parent at recess has over students. Plus tackling.
The courtroom is your playground, and you're in charge of keeping order. But just like the teacher who answers to principals and statewide exams, you have judges and attorneys and even federal jurisprudence telling you what to do and reminding you of the limits of your power.