The difference between sound and meaning, must be underspecified. Without underspecification there would be nothing left to say because everything would already have been said. This problem is solved with the difference between words and sentences. Words are also constellations of sounds with meaning; but they do not determine the sentences that they can produce when combined.... With the help of speech, one may say something that has never been said before.
Why speech is so advanced. It is a system/combinaison of meaning that create larger, more complex meanings. Without language, we are unable to express or even understand complex meaning, especially abstract.