I was wondering why he wanted the reader to see events through Huck's eyes.
Twain was quoted by the literary critic Alfred Kazin as saying that he set out to write his adventure novels to remind adults of what they used to be - children.
With this in mind, Twain's choice to present a story through the mind of a boy makes perfect sense. Not only are the actions and attitudes of childhood often different from adulthood, but so is the mind of a child different from the adult he or she becomes.
I can't give you three examples, but I think Mark Twain wrote The Adventures of Huckleberry Finn through Huck's point of view because he recognized the most powerful record of the events in the novel would be delivered first hand, by Huck himself, as the events occurred. From the first sentence, the reader is listening to Huck relate the story of his adventures in a very conversational tone.
You don't know about me, without you have read a book by the name of "The Adventures of Tom Sawyer," but that ain't no matter.
As the story proceeds, we are given insight into how Huck perceives people and events and we observe the changes in his thinking that develop as a result of his adventures. This is probably most obvious in the changes in his attitude toward Jim, as he evolves from thinking
Once I said to myself it would be a thousand times better for Jim to be a slave at home where his family was, ... and so I'd better write a letter to Tom Sawyer and tell him to tell Miss Watson where he was
Somehow I couldn't seem to strike no places to harden me against him, but only the other kind. I'd see him standing my watch on top of his'n, stead of calling me, so I could go on sleeping;...I shoved the whole thing out of my head; and said I would take up wickedness again, which was my line, being brung up to it, and the other warn't. And for a starter, I would go to work and steal Jim out of slavery again;
The revelation of his innermost thoughts could never be more clearly conveyed than in Huck's own words.