Rok, thanks. I can't disagree with you about anything in your post; save for the IMPLICATION that having the training and being polished precludes being able to convey emotion. Clearly there are performers that were born with "the gift" and can get the message across wether they have the training or not. I don't know much about Mahalia Jackson's background to know wether she had any training or not; I just know how much I love her singing. But, the flaw in your argument is not in the substance of the general point, but in the specific example. Saying that Kathleen Battle singing spirituals doesn't move you the way that Mahalia Jackson does proves little. Have you ever heard Mahalia Jackson sing Schubert Lieder? I haven't either, but I am fairly confident that it wouldn't make me cry the way Battle can. This a common mistake by performers; singing or playing in a genre outside their comfort zone.
http://m.youtube.com/watch?v=4Qki5oy1z14
http://m.youtube.com/watch?v=4Qki5oy1z14