For me, the most important quote in this book regarding identity comes in Chapter 22, when Antonio is having a conversation with his father about the conflict he has been facing throughout the novel. He has faced the expectation and desire of his mother him to become a priest and follow the Luna side of his family, but equally his father has wanted him to become a Marez, and to dwell itinerantly on the plains. Equally, he has felt torn between the Catholic religion and a more pagan religious belief represented by the golden carp. In this conversation, he finally understands that he does not have to pick one and reject the other, but can in fact incorporate elements of both into who he is as a person:
"Then maybe I do not have to be just Marez, or Luna, perhaps I can be both--" I said... "Take the llano and the river valley, the moon and the sea, God and the golden carp--and make something new," I said to myself. This was what Ultima meant by building strength from life.
This is a vital moment in the story as Antonio sees a way of resolving the intense conflict that he faces as he can "make a new religion," incorporating pieces of all of the heritages he has grown up with. He sees that identity can be composite and does not have to be absolute.