What is the author's overall theme in Bless Me, Ultima and what scene in the book supports that theme?

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.