Ultima is a complex character. She is a devout Catholic who attends mass regularly and at the same time she is known as a medicine woman (or healer) who uses natural remedies and even "spells" to treat the many maladies brought to her as a Curandera.
She believes that the plants, the river, the plains, and other parts of nature all have spirits of their own. She also believes that nature has the power to heal and she harnesses that power in her role as a healer. She is respectful of nature and Antonio models this same behavior. She teaches him to find the value in all that nature has to offer.
Antonio is drawn to Ultima for many reasons, but her connection with nature offers him a different view of the world around him than he is getting from anyone else in his family or church. While his mother's side of the family is from the llano and values the land, the only person really demonstrating a true and tangible connection to the land is Ultima. Antonio's relationship with Ultima helps him to connect with the land and with his own abilities to heal.