Delivery or body communication can contradict the message or spoken word of a speech when it does not match the mood of the speech. For example, if a speaker is giving a speech about their favorite meal, we would expect them to have a positive attitude and be expressive about things that particularly excite them, but if instead the speaker had a somber tone and seemed overall disinterested, then the audience would be less convinced of the fact that this is their favorite meal. Contradictions in this manner result in diminished credibility and potentially the loss of the audience's attention. When looking back at the example of a person's favorite meal and the contradictory delivery and body communication to the speech, the audience would not only be poorly convinced that this is their favorite meal, but would also be less interested in even hearing about the meal as a whole. In summary, when body communication or delivery and the speech do not match up, the speaker loses both credibility and the audience's attention.
I agree, it would be counterproductive to bring up something that you care about, yet giving a speech and acting like you don't care at all. Without the right delivery or body communication, it would seem like you didn't care about the topic at all.
I really liked the specific example you gave about someone's favorite meal. I also agree that the audience can lose interest if the tone doesn't match the message. Very good vocabulary as well!