Besides helping your audience remember something, repetition builds greater awareness of central points of the main theme. Often, repetition contributes to the flow of the presentation. Do not be afraid to repeat the main point of your presentation. The best quotations are short and memorable. They not only say something meaningful, but they say it clearly.
Good quotes work on several levels, forcing the audience to think.
Make sure the quote is clearly attributed and that it was said by someone your audience will probably recognize. Quotations are often particularly effective at the beginning or end of a presentation but can work well almost anywhere. Startling or surprising moments. Surprise is used to draw attention to the point you are about to make. Saying something the audience is not expected to hear can reawaken the audience.