Have you ever been faced with two choices? It could be anything: Which guy should I ask to the dance? Do I want cheese or pepperoni? Instead of just going with your gut, do you ever take some time to sit there and weigh your options? Probably not often enough. But that's what Antonio does almost all of the time when faced with a decision or a question with more than one possible answer.
Thought drives Antonio. There are moments when he takes action, but at the end of the day, it's all about mulling questions over and thinking through the various possible answers to those questions. That's what moves Antonio and the novel as a whole forward.
One of the first questions Antonio poses comes when he asks his mother, "'Was Ultima at my birth?'" (1.271). Sure, this might be a simple yes or no question on the surface, but Antonio is really asking about his destiny (or his "density" for all you George McFly fans out there). In his dream, Antonio has seen his mother's family and his father's family arguing over his future, and he has seen that the woman who delivered him (yes, it turns out to be Ultima) might be the only one who knows what lies ahead for him.
Questions about his future and the powers leading him along his path practically plague Antonio throughout the novel. This idea that questions and thoughts about the nature of the world drive Antonio is demonstrated quite literally in the Catechism scene, where we get to see the priest ask some big time questions to Antonio and his classmates. Questions like, "Why did God make you?" (17.354).
But, these kids' answers to these questions amount to no more than rehearsed responses. While most of the other kids might be okay with that, our boy Antonio needs more (as if you didn't see that coming). He has to think about what all of the possible answers to the question are and whether or not the question even has real meaning. Sheesh. Ah, but such is the life of a kid obsessed with thinking in a novel with a thoughtful tone.