What rhetorical features in the Preamble reveal the purpose of the Constitution? What is the purpose?

Repetition and Parallelism.

The preamble of the Constitution contains the rhetorical features of repetition and parallelism. The repetition occurs with the words "United States." We can see "United States" in the beginning and at the ending of the preamble (which is actually only one sentence). Parallelism, as you may know, is when a list/series has all elements with similar pattern or structure. For instance, if one element of a series is a phrase that is comprised of a verb and a noun, then, in order to be considered parallel, all elements will contain a verb and a noun. Let’s look at one element of the preamble: "establish justice." "Establish" is a transitive verb, which requires a direct object (noun). That said, "justice" is a noun and direct object of the verb "establish." What makes the Preamble parallel is that each series/list item contains a transitive verb and direct object. The purpose of beginning and ending the Preamble with "United States" is most likely to stress for what the constitution will stand-The United States of America. The purpose of the parallelism is most likely to stress that all series items are tantamount-are or equal importance. As for the overall purpose of the Preamble, what it does is disclose the reasons for the creation of the Constitution; it also outlines the exact powers of the future government and mentions the source of powers-the people of the United States of America.