Speakers should always be motivated by their desire to please the audience; audiences are motivated by their own self-interest. Both forms of self-interest come together well if you realize that every person you're talking to is thinking, "Why should I care about this speech?" Everyone has a secret radio station called WIIFM, otherwise known as "What's In It For Me?" An effective speaker anticipates this built-in bias and shapes a speech by always thinking, "What benefit or benefits can I offer this particular audience?"
You sell an audience with benefits, not facts. To use the old expression, you buy a drill not for the drill but for the hole it will make. A ballpoint pen has a retractable point (fact), so you don't get ink on you (benefit). But be careful of just throwing benefits at your audience; the connection between the product and the benefit—in this case the retractable point—must always be clear, because that's often the item or outlook you are trying to promote. Never assume that the members of the audience will make the connection themselves.
At first glance, this advice may sound cynical: People are so narrow-minded that everything must be fed to them in terms of self-interest. Not everything; just your speech. Think about it from this perspective: As a speaker, you are taking up people's time; you are asking them to listen closely to you for a period of time and to think hard about what you are saying. It may be cynical (and practical) to appeal to their needs, but it's also polite. They are giving you their time; you must respond with something worthy of that honor. In the end, everyone benefits, especially you, because you will have succeeded in making your points in a vivid, convincing, and memorable fashion.