Parallel structure guarantees uniformity and consistency throughout a piece of writing, to ensure its clarity and accuracy. And by making each compared item or idea in a phrase or clause follow the same grammatical pattern, you create a parallel construction.
We need parallel structure because it makes a piece of writing easier to understand. Parallel structure allows us to understand when things are taking place, what is taking place, who or what the subjects and objects of a sentence or clause are, and so on. And when writers follow a parallel structure, they are less prone to making common grammatical errors.
Parallelism is important in writing because it allows a writer to achieve a sense of rhythm and order. When sentence structures are not parallel, writing sounds awkward and choppy.
Parallelism also helps the writer ensure that his entire sentence is in active or passive voice.
