Final answer:
Parallel structure, or parallelism, is important because it helps create symmetry and balance within sentences and emphasizes ideas. It is used in writing and speech as an organizational strategy and to make ideas more memorable and engaging for the audience.
Step-by-step explanation:
Parallel structure, also known as parallelism, is important because it helps create symmetry and balance within a sentence, making ideas easier to remember and pleasing to the ear. It involves using similar or equivalent constructions of phrases or clauses to emphasize an idea. For example, in President John F. Kennedy's inaugural address, he used parallelism to emphasize the idea of collaborative work for the success of liberty. Parallelism can also be used as an organizational strategy and to emphasize ideas in writing or speech.