Perhaps the most important consideration in the selection of a topic and in writing your speech is the purpose. What do you want the audience to do or think or feel as a result of what you say? This is a question you should ask not only yourself but also your sponsors. They had a reason for inviting you to speak and they ought to know what they want the speech to accomplish.
It is a good idea to write down a brief statement of purpose and keep it at hand as you write your speech.
From my experience in reading and writing speeches, I have concluded that there are six basic purposes of a speech:
To convince or persuade
These can overlap, and of course a speech can have more ...