Perhaps something more frightening is going on here? Perhaps the devil really does exist, and Ivan is in fever because he has seen him?
I for one was persuaded by the argument that the devil exists and is necessary to man. Let me find it in my notes… Here: “By some pre-temporal agreement, which I have never been able to figure out, I am appointed ‘to negate,’ whereas I am sincerely kind and totally unable to negate. No, they say, go and negate, without negation there will be…nothing but ‘Hosannah.’ But ‘Hosannah’ alone is not enough for life, it is necessary that this ‘Hosannah’ pass through the crucible of doubt…Live, for without you there would be nothing. If everything on earth were sensible, nothing would happen. Without you there would be no events, and there must be events…” (642). Without the devil, there would be no suffering. And suffering is necessary, is it not, if we are going to understand the purpose of God?