The introduction of the speech should be appropriate to situation and the message.
If at a funeral, your speech begins with an introduction that sounds merry and cheerful, it won't be acceptable. Or on the other hand, if your speech at a youth festival begins with a sad and philosophical introduction, the audience would lose interest. The introduction should only outline the context of the topic, it should not be deeply explained.
Thus, how well you keep the audience engaged in your speech primarily depends on how well you introduce the topic.
