Within the world of the novel, Dust is an elementary particle that collects around adult humans beginning at the onset of puberty, as a person's dæmon begins to settle. It is a physical embodiment of adults’ capacity for individual choice as they lose their childhood innocence and gain knowledge of the world—whether those choices are good or evil. Because of this, the Magisterium decides that Dust is both proof of and the reason for original sin, or the ability to make choices and acquire knowledge (and also is the root of death, disease, and evil). Turning original sin into a physical thing that can be studied, manipulated, and blamed for the world's evils magnifies the Magisterium's need for power, as it means that there's a way to create a population that's easier to control: stopping Dust from settling, and original sin from taking hold, through intercision.
Dust Quotes in The Golden Compass
Ever since Pope John Calvin had moved the seat of the Papacy to Geneva and set up the Consistorial Court of Discipline, the Church's power over every aspect of life had been absolute. The Papacy itself had been abolished after Calvin's death, and a tangle of courts, colleges, and councils, collectively known as the Magisterium, had grown up in its place.
"I think he's got an entirely different idea of the nature of Dust. That's the point. It's profoundly heretical, you see, and the Consistorial Court of Discipline can't allow any other interpretation than the authorized one. And besides, he wants to experiment—"
"To experiment? With Dust?"
"If he's got Dust and you've got Dust, and the Master of Jordan and every other grownup's got Dust, it must be all right. When I get out I'm going to tell all the kids in the world about this. Anyway, if it was so good, why'd you stop them doing it to me? If it was good, you should've let them do it. You should have been glad."
"She guessed that the two things that happen in adolescence might be connected: the change in one's dæmon and the fact that Dust began to settle. Perhaps if the dæmon were separated from the body, we might never be subject to Dust—to original sin."
"We've heard them all talk about Dust, and they're so afraid of it, and you know what? We believed them, even though we could see that what they were doing was wicked and evil and wrong...We thought Dust must be bad too, because they were grown up and they said so. But what if it isn't? What if it's—"
She said breathlessly, "Yeah! What if it's really good..."