Authors are spoken about as one who can turn a phrase, that's grammar. The art of persuasion is grammatical. Authors revel in grammar when they write. Teachers use grammar when analyzing literature. They show patterns, that is grammar.
Readers can follow arguments that are well written because of the grammar.
Parallelism is an important writing tool because it provides reader clarity. The reader needs parallelism to interpret. Grammar is a major tool to the essayist. I recall, on NCTE-Talk a three line ditty about woman without man or something like that. Each sentence was punctuated differently resulting in third distinctly different sentences but with the same words.