If we ever want to share an idea or get something from someone, we are going to have to learn to communicate. In order to get our idea or request across, we'll need to be able to put that idea or request into a form that someone else can understand. This is why talking and writing are so important.
I was watching a video of a dramatization of some native people trying to barter with a someone from a trading post. They used no words in the video. My students asked if they didn't talk back then, but someone realized that they probably did not speak the same language. I pointed out that they were still communicating because they both knew that the First Nations people wanted good like blankets and tools, and the storehouse owner wanted their furs. It was just a matter of how much. Being able to speak the same language definitely cuts down on the confusion and misunderstanding. (Though not all the time. See: Married People, Politicians, Lawyers, etc.)
Some of the things I teach my students under the umbrella of communication are: talking, listening, writing, reading, looking, asking questions, interpreting and evaluating information (Does this make sense to me? Does this fit with how I see the world?), drawing, acting, creating presentations, learning a new language, reading people's moods and body language, role playing, sharing, debating, arguing, playing music, making posters and signs, etc.
Perhaps if we lived our entire lives by ourselves we would not have the need to communicate. But perhaps not. Sometimes, just putting our own thoughts into words helps us understand something or work out a problem. Recently, my friend KA told me that he knows that he processes things by talking. So by giving kids words, I guess for some we are really giving them the vocabulary for thinking as well.