how does diction affect theme in a story?

Some scientists say that diction is 40% of our communication. The other 40% is body language, words are just 20% (the values may vary a little bit among different research). So if one has a poor diction and we can't see his body language (i.e. in audiobooks), we will get just 20% of the theme, and it can largely affect our imagination of the story.