In the introduction to Notes From the Underground (introduction by and translated by Pevear & Volokhonsky) Dostoevsky says that the Russian censors allowed him to abuse the entirety of Russian society, but when he tried to explain the need of religion in the human soul they cut it out. To me it seems that Alyosha is the embodiment of this principal he was not allowed to explicitly state. Perhaps that people need something to look up to. They need a carved snake on a pole to look for when live ones bite. Speculation.
It's also the sort of novel that doesn't dissect well. In order to convey the correct sense or feeling or reason for an action or statement, I would pretty much have to drag you back to chapter one and work my way up. I will revise that to say that it doesn't vivisect well, because The Brothers Karamazov is as close to a living inanimate object as I have ever seen.
Today's art is an onion. If this piques your curiosity, please look up "Dostoevky's parable of the onion."