Listening is difficult. Your audience is likely to start with considerable goodwill towards you (not least because they're grateful that it's you speaking and not them), and they listen at first in the hope of finding that you've chosen an interesting subject about which they may learn something. If they can easily hear what you say, they will tend to go on listening, and if you are obviously interested in what you're saying, they will pick up on your interest and so be willing to carry on listening (which is why, later, we'll stress the importance of your enthusiasm). If you speak slowly, they will have time not only to hear what you say, but also to understand and assimilate it, make it part of their own knowledge base and, perhaps, think of a useful question to ask. If you speak quickly, there simply isn't time for this process to take place, even if they manage the first part, hearing, or even the second part, understanding, they won't have time to assimilate the information and make it theirs. As a result, they will remember very little and will feel that they have gained no long-term benefit from being present.

(Emden & Becker Presentation Skills for Students, London, Palgrave, 2nd edn. 2010/2016, pp.12-13)

Extra point for consideration: what Register is this text written in? What language features reveal this?