When you've got a character as interesting as Marcelo, why wouldn't you write from inside his brain? His internal music is reason enough to dive into his mindset whole hog. Because he sees the world so differently from other people, he helps us to see it differently, too.
One way Stork takes us into Marcelo's brain is by writing very formally. For example, Marcelo refers to himself and the people to whom he's talking in the third person. Instead of saying, "It's hard for me to look at women the way you do," he says, "It is hard for Marcelo to look at women the way Wendell does" (12.28).
And that's another thing: he doesn't say "it's"; he says "it is." Most people speak with contractions, so when Marcelo doesn't, it makes him seem almost robotic. Like when he says, "Suffering and death do not affect me the way they seem to affect others." (4.34) If you said that sentence, you'd probably say "don't" instead of "do not." It's a very formal, very alien way of speaking that sets Marcelo apart from the real world and the other characters who live in it.