The Russian playwright Anton Chekhov has a famous rule about how objects are used in literature: "If in the first act you have hung a pistol on the wall, then in the following one it should be fired. Otherwise don't put it there." And boy, is there ever a giant bazooka hanging on the wall of this novel.
When Myshkin goes to Rogozhin's place, just after Nastasya flees from them both to Petersburg, the two men have a really weird scene where Myshkin keeps picking up a knife that Rogozhin just happens to have lying around and Rogozhin keeps slapping it out of his hands (2.3). Like, this happens more than once. Well, guess what? All that's missing is a giant neon arrow blinking and pointing at this knife with a buzzer going off every time it lights up. The knife is important. It will be used to stab someone. Keep an eye on it.