First, it helps you to think more clearly and to pursue your ideas in a more systematic way. Organizing your thoughts in a clear, coherent, and logical manner is one step to becoming a good critical thinker, someone who can reflect upon their own ideas and analyze others'. Second, organization increases the likelihood that your speech will be effective. Audiences are unlikely to understand disorganized speeches and unlikely to think that disorganized speakers are reliable or credible.
Speeches have two types of structure.
The introduction of the speech establishes the first, crucial contact between you and your audience. For classroom speeches, it should last less than a minute. The introduction is the place where you should state your main claim or idea very clearly and give the audience a sense of what you aim to do or accomplish in the speech. You need to orient your audience and make connections between what they know or are already interested in and what you are speaking on. Establish goodwill and credibility.