The use of literary techniques (or literary/poetic devices) are sometimes necessary in a work in order to allow the reader to relate to the piece. Sometimes, if a text lacks the use of literary devices, a reader can fail to engage with the text based upon their inability to relate or understand what is being presented.
In regards to Isabel Allende's novel Eva Luna, one literary technique which is used to engage readers is imagery. Imagery is the author's inclusion of descriptions which appeal to the reader's senses in order for the reader to create mental images of the material (such as characters and setting) presented.
On the first page of the novel, the narrator (Eva) states the following:
My name is Eva, which means 'life,' according to a book of names my mother consulted. I was born in the back room of a shadowy house, and grew up amidst ancient furniture, books in Latin, and human mummies, but none of those things made me melancholy, because I came into the world with a breath of the jungle in my memory.
Here, readers can picture the home Eva grew up in. The use of descriptive words, such as "shadowy," "ancient," and "human mummies" provides readers with a very distinct picture.
Eva then goes on to describe her parents:
My father, an Indian with yellow eyes, came from the place where the hundred rivers meet; he smelled of lush growing things and he never looked directly at the sky, because he had grown up beneath a canopy of trees, and light seemed indecent to him. Consuelo, my mother, spent her childhood in an enchanted region where for centuries adventurers have searched for the city of pure gold the conquistadors saw when they peered into the abyss of their own ambitions. She was marked forever by that landscape, and in some way she managed to pass that sign on to me.
Readers can see the yellow eyes of her Indian father, the smell of earth on him, and the light shine upon him. For Eva's mother, readers can picture the place where she grew up (images similar to the likes of the painting "Meeting of Cortés and Moctezuma").
In the second paragraph, of the first chapter, one can identify Allende's use of both the metaphor and the simile (used when describing her mother as a young child):
Missionaries took Consuelo in before she learned to walk; she appeared one day, a naked cub caked with mud and excrement, crawling across the footbridge from the dock like a tiny Jonah vomited up by some freshwater whale.
Here, the comparison to "a naked cub" provides not only an example of a metaphor, but a picture with which readers can engage with. The simile appears in the comparison between Eva's mother and Jonah (given the use of the word like).
Essentially, Allende's use of metaphors, similes, and imagery allow the reader to respond to the text based upon their engagement with it (through the reader's ability to actually picture what is being described).