We don't ask why God chose as his prophet a stutterer with a public speaking phobia. But we should. The book of Exodus is short on explication, but its stories suggest that introversion plays yin to the yang of extroversion; that the medium is not always the message; and that people followed Moses because his words were thoughtful, not because he spoke them well.
Quiet: The Power of Introverts in a World That Can't Stop Talking (ed. Broadway Books, 2012) - ISBN: 9780307452207