Establishing your purpose is the beginning of the fine-tuning all good speakers do. And the same purpose can lend itself to talks with very different thrusts, depending on your audience. For example, a talk on leadership to senior executives will differ from one to new managers. The thrust may change from reinforcing to introducing; the examples relevant to the audience's business life will be different. Other shifts would occur if you prepared a talk on the same topic to laypeople and technical experts.
Should speeches be entertaining, strictly technical, or a little of both? Speeches have their own tenors that can either be inappropriate to the subject at hand or just fight. The twist you put on the facts will guide much of your audience's reaction to the information you're imparting.
A plea for humor: Even if your purpose and your tone are extremely serious, you shouldn't neglect the saving grace of humor. An amusing example or story is still one of the best ways to be memorable; even Shakespeare had comedy in the midst of his most tragic plays. I am not suggesting you work at being a stand-up comic, but that you take advantage of the bond created when speakers get audiences to laugh with them.