Poems that utilize the grammatical principle of parallel structure include repetition of words or phrases to show that two or more ideas have the same level of importance. Parallel components in a sentence are grammatically identical or similar in their construction, sound, meaning or meter.
In poetry, parallel structure can be used to create a flow of images or observations that establishes a definable rhythm or sound. That sound parallel can be alliterative, which is similar in sound, or by length and rhythmic stress, as in "government of the people, by the people and for the people."
Antithesis, a rhetorical technique in which two opposite ideas are put together to achieve a contrasting effect, is a common form of parallelism. English poet Alexander Pope uses antithetic parallel structure in "An Essay on Criticism" with the line, “To err is human; to forgive divine.” Pope is saying that imperfection is inherent in the human condition, and forgiveness is an action associated with God, or the realm of the divine. Through these antithetical but parallel structures, the poet is able to relay that God is so forgiving because his creation is so imperfect.
Writers, preachers, politicians and comics can utilize parallel structure in the rhythm and repetition of their language as a tool of persuasion that emphasizes passion, strength of voice and power.