But then I wonder, "Why Maurice?" Clive must have figured out that his newfound friend wasn't the "brainy sort," especially after he debunked Maurice's supposed religious views.
Yes, that's a very good question. Maybe he's the one person who sees the hidden qualities in Maurice that no one else at this point does, not even Maurice. And Maurice has certain intensity even if he's not quite up to Clive in intellectual depth. There must be something that inspires Clive to be bold enough to make the move and I don't think perceived (or projected) similarity of background doesn't quite seem enough.