Every individual must choose his or her own path. This is one theme expressed in the novel. We can see this theme both as Antonio's challenge and as the lesson Ultima tries to emphasize to Antonio.
The idea of Antonio's future is debated repeatedly by Antonio's parents. His mother wants him to become a priest. His father wants him to continue the Marez tradition and become a vaquero, roaming the vast planes of the southwest. Antonio is conflicted about his own vision, wanting to please both of his parents but recognizing the impossibility of doing so.
This conflict is symbolized in the story's setting as well.
The house in which Tony’s family lives represents these two conflicting ways of life: while they have settled onto a piece of land where they have a small farm, they are just on the border of the llano.
Where Antonio's parents create a conflict in Antonio regarding how to choose his future path, Ultima tells Antonio that he will need to make decisions for himself.
“I cannot tell you what to believe. Your father and your mother can tell you, because you are their blood, but I cannot. As you grow into manhood you must find your own truths.”
We see in this moment a rather full articulation of the theme of the need for the individual to choose his/her own path. Though Antonio does not come to a final or conclusive position concerning his future by the end of the novel, he does accept the fact that he will have to be the one to decide on that future. He learns that the responsibility lies with him.