Hello. You did not enter the speech to which this question refers, which makes it impossible for your question to be answered accurately. However, I will try to help you in the best possible way.
To identify the main message of a speech, you must understand the subject that is being discussed in the speech and how that subject is developed by Ban through the arguments of the speech. Likewise, to identify the evidence, you must consider the information that the author uses to justify the arguments he presents. This is because the evidence is used to give veracity and prove that the author uses correct and relevant arguments to develop the theme of the discourse.