Final answer:
The literary device used in the phrase from Macbeth is a metaphor, representing Macbeth's troubled thoughts. Furthermore, repetition is a rhetorical device that adds emphasis and can indicate motifs or themes within a text.
Step-by-step explanation:
The literary device used in the excerpt "O, full of scorpions in my mind, dear wife!" from Shakespeare's play Macbeth is a metaphor. This metaphor is used to represent Macbeth's tormenting thoughts and the mental agony they cause. The comparison of scorpions in his mind implies that his thoughts sting and are as troubling as a swarm of scorpions would be. Metaphors create vivid imagery for the reader, allowing a deeper emotional connection to the characters and their experiences. They also encourage us to make new connections and discover new ways of thinking about the relationships between different elements, such as a character's emotions and their symbolic representation.
Regarding repetition, it is a powerful rhetorical device that enhances a narrative by giving emphasis and can signify motifs, themes, or emotions. A repeated word or phrase gains importance and alters the reader's focus and interpretation of the text.