Seth Godin shares this insight in his blog. It is dead on when giving a talk. Last week we mentioned finding your voice by listening to great story tellers. Godin takes the counter example.
Your voice will give you away
It's extremely difficult to read a speech and sound as if you mean it.
For most of us, when reading, posture changes, the throat tightens and people can tell. Reading is different from speaking, and a different sort of attention is paid.
Before you give a speech, then, you must do one of two things if your goal is to persuade:
Learn to read the same way you speak (unlikely)
or, learn to speak without reading. Learn your message well enough that you can communicate it without reading it. We want your humanity.
If you can't do that, don't bother giving a speech. Just send everyone a memo and save time and stress for all concerned.