Final answer:
The phrase "A river of moral red" is an example of a metaphor, which directly compares two unlike things to suggest a likeness without using 'like' or 'as'. Metaphors, alongside similes, are key literary devices in literature that create vivid imagery and deepen the reader's understanding of an idea or concept.
Step-by-step explanation:
The literary device exemplified by the phrase "A river of moral red" is a metaphor. A metaphor is a figure of speech that compares two unlike things directly, without using 'like' or 'as,' which are traditionally used in similes. Metaphors and similes are both means of comparison that help to illuminate and expand upon ideas or concepts in literature.
When analyzing literature, it is important to pay close attention to the usages of various literary devices. Metaphors, such as the one presented in the question, facilitate a deeper understanding of the text by creating a vivid mental image. It encourages the reader to perceive and consider abstract or complex ideas in a more tangible manner.