Spouse of a U.S. Vice President and Senator and later a Senator herself, Muriel Humphrey once told her husband, "Hubert, a speech doesn't have to be eternal to be immortal." She certainly made a good point about speeches and presentations that last too long. But there's also a point to be made about the ending itself.
Actually, there are several points.
A persuasive ending has two key elements, a call to action and a reason to act. At the end of a presentation, for example, you may need to request the funding, close the sale, or push the new initiative. You have to motivate your listeners to respond positively to your call by giving them good reasons to do so.
The call to action represents the main purpose of your communication, so make it concrete. Your audience needs to know what to feel, think, or do as a result of having heard your presentation. Evoke or recognize the feeling, articulate the thought, suggest the things you want listeners to do.
Make certain that you link this call to action to a solid reason to act, a reason that matters to your audience, not necessarily to you.
Not every presentation requires a dramatic conclusion, but you are more likely to get what you want when you close strongly. Strive to link a clear call to action to a clear benefit to your listeners.
Calls to action that begin with "I want you to..." or "I urge you to..." are usually not very effective. They are certainly not very strategic. Audience members care most about what is in it for them. People are motivated to act when they see that doing so will benefit them, that doing so aligns with their own interests or meets their own needs.
If you're asking for money for your new initiative, then, don't tell them how much you need the money but how much they need the initiative. Give them a reason to act. Emphasize that your initiative will provide security by growing business. Emphasize that it will increase job opportunities. Emphasize that it will fill a demonstrated need. These are all reasons to act, and weaving such reasons into your closing helps listeners identify how a positive response will be to their benefit.
If it's possible, use your very last words to circle back to the opening of your presentation, back to the grabber with which you began your talk (see how to open a presentation). Doing so will help listeners place those introductory words in the context of all you have just said. But it will also provide them a sense of closure, an ending to the story of your presentation. Best of all, it supplies you with a graceful exit, the kind that Muriel Humphrey was perhaps suggesting more speakers should make.