Final answer:
The poetic device in question is known as a 'refrain', which is a repeated phrase, line, or group of lines in a poem, reinforcing themes and rhythms. It's akin to a chorus in a song and serves to unify the work while setting expectations.
Step-by-step explanation:
The poetic device described in the question is known as refrain. A refrain is a phrase, line, or group of lines repeated at intervals throughout a poem, commonly at the end of each stanza.
Its purpose is to reinforce the themes and rhythms of a poem, much like a chorus in a song. Repetition, in general, is a powerful rhetorical device and can be spread throughout a text to create a motif, which is an element that repeats to contribute to the thematic significance of the text.
For example, the use of the phrase "I have a dream" in Martin Luther King Jr.'s speech serves as a refrain to emphasize the theme of equality and hope for the future. In literature, such as in F.
Scott Fitzgerald's The Great Gatsby, the repeated reference to the green light serves as a motif for Gatsby's elusive dream. Repetition and refrain can create rhythm, build suspense, and emphasize important ideas, unifying a text and setting expectations for the reader.