As an older Antonio narrates, his younger self quickly emerges as the protagonist of the novel. We mean, why tell a story if you're not going to talk about yourself, right? And this is Antonio's tale through and through. If you're looking for a fancy word to throw around, you could call Bless Me, Ultima a bildungsroman. That's just a literary way to say this book tells the story of a young man coming of age.
Antonio's power and his struggle come from the fact that he questions everything. He seeks answers about everything from his future to his past to the nature of God:
"Papa," I asked after a while, "why is there evil in the world?"
"Ay, Antonio, you ask so many questions." (22.176-178)
That exchange serves as a pretty good example of conversations that take place throughout the novel, as Antonio's desire for self-discovery drivse his journey through the book.
The contrast to the thoughtful, wise-beyond-his-years Antonio is normal-kid Antonio. He fears the first day of school, he gets into some fights, his sisters annoy him, and sometimes he just wants to go fishing. This normalcy, though, doesn't change the fact that he's a special guy. Ultima knows he has power and understanding beyond most children, and even the other kids look to him to serve as their mock priest when preparing for their first confession.
As this is a bildungsroman (Boom! Used the fancy word again), Antonio must come of age and grow into a man by the end of the novel, and it just plain has to be all about him.