He is a Márez, the vaqueros shouted […] He is his father's blood! (1.190-192)
Dealing with the claims that his parents' families lay on Antonio from the moment he comes into the world is at the very heart of who this kid is, the struggles he faces, and the journey he takes.
Only I will know his destiny. (1.198)
Well someone's getting territorial. Antonio hears Ultima say this in the dream he has about his birth, before Ultima ever even shows up to the joint (and already she's staking her claim). With this little tidbit, Anaya establishes the deep connection between Antonio and Ultima, and he grants Ultima a pretty heavy dose of power. She is the only character who can truly see how another human being's life will turn out. At least, that's what Antonio seems to think.
I saw the old woman who had delivered me from my mother's womb. I knew she held the secret of my destiny. (1.411-413)
Obviously, this ties into what Antonio sees in his birth dream. More importantly, though, it demonstrates that one of Antonio's driving obsessions when he was very young is discovering his fate, which is a little existential for a tiny tot like him.