Knowing a lot of vocabulary, and using perfect grammar MEANS NOTHING if nobody can understand you. Pronunciation is the most important part of your English language study.
Hi funtoys! I think what the sentence is saying is even if one has a rich vocabulary and excellent grammar, if s/he mispronounces most words then s/he cannot be understood. You have to read the complete sentence to get the thought conveyed, and not break it up and interpret it as you like.