What is the theme in The Idiot by Fyodor Dostoevsky?

Religion plays a big part in this book. Most of the characters see themselves as religious and mistrust anyone who claims to be atheist. Dostoevsky shows this when nihilists visit the Prince, and the characters all turn on them, claiming they are nothing but scoundrels. Interestingly, these nihilists are part of the younger generation, which the older characters reject because they think their liberal ideas are destroying traditional Russian values.