Final answer:
Repetition is the rhetorical device mainly used to emphasize an important point.
Step-by-step explanation:
The rhetorical device mainly used to emphasize an important point is repetition. Repetition involves repeating a single word or group of words to build emphasis. For example, one might use repetition to convey the significance of an idea by restating it multiple times. This rhetorical device is often employed in speeches, poetry, and persuasive writing to make a point more memorable and impactful.