The development of language gave early societies a whole new layer of reality apart from just what we saw around us. That is clearer than ever with the internet, since we now fling words around the world that are completely separated from our actual bodies and environments. So its no wonder that we have imbued words with magical powers ever since words were a new thing.
Spells, incantations, and magic words are all used for storytelling, religion, and a lot of entertainment, as well as everyday communication. The fact that we have words to communicate with is fairly astonishing in itself, so it's no wonder that words can be thought of as supernatural. After all, they do affect reality. Words can inspire, charm, or hurt people, and they can't be taken back. Words make up vows, testimony, propaganda, education, memories, laws, and history, and all those are pretty important. Dr. Erica Brozovsky of Other Words (previously at Neatorama) goes through the history of magic words, and then explains how words are still used for their power to change reality.