The introductory part of a speech primarily aims to reveal the topic or subject matter to the audience and provide a preview of thesis of the key ideas that are going to be discussed throughout the entire speech as this not assists in capturing the audience's interest and attention but also in establishing the credibility of the speaker(knowledge reflected in the revelation of topic and thesis).
As per the question, the given example demonstrates the 'previewing of key ideas' aspect/purpose of the speech introduction as it reveals the subject matter and its key aspects('I will discuss the scientific.....of alternative medicine') that are going be discussed throughout the speech among the audience. This statement aware the audience about the content that is going to be presented to them that not only seeks their attention but the interest as well.
