A good speaker has this purpose: the people who attend my presentation will leave "better" than how they arrived.
They now look at something from a different perspective: "Oh! I never thought of it that way. That makes sense!"
They learned something: "So that's why we should distribute handouts after our talk instead of ahead of time!"
They became curious: "I can't wait to google 'vocal fry' to learn more about that contagious speech phenomenon Pam talked about."
They became indignant: "I didn't realize illegal dumping was happening in our town. I'm going to do something about that!"
They got inspired: "If she can overcome her fear of having 'all eyes on her,' I can too!"
Decide ahead of time how you want to make a difference and craft your presentation to make that happen. Create an effective call-for-action and state it loudly and clearly.