I read the quote in Alyosha's voice, I don't remember if it's really him. I'm by no means a Dostoyevsky expert and I read the book, halfheartedly, a long time ago. So please do your own thinking when I say that Ivan, not Alyosha, is closest to the author's heart.. he wrote about the three brothers because he was trying to resolve the conflicts between (at least) 3 archetypes of the Russian soul! Too humble he was, to try to generalize that to the world, but the downside is, later readers can't help but put in their own interpretations, or selectively quote stuff that aligns with their lonely hearts..

I believe those words are said by the elder Zosima in one of the early chapters when he has several visitors. Not Alyosha - although it's been several years since I've reread the book.