Without symbolism, something essential is missing from language and art. Symbols allow authors to impart ideas above and beyond the literal level of the text. A symbol represents, or stands in place of, something else. Even letters and words themselves are symbols, because our brain turns those markings into thoughts and ideas.
Symbols are everywhere in our lives. Traffic signs, advertising logos and religious iconography all provide visual information that transcends the physical world. Think of the Apple logo--It's really very simple, silhouette of an apple with a single leaf at the stem and a small bite taken out of the top. Show that logo to nearly anyone in the world, and they will immediately recognize it. The Apple logo represents a whole network of products, images and emotions. Amazing doesn't begin to describe what our mind is capable of doing in terms of converting a simple image into something utterly profound.
There are culturally based symbols, like a nation's flag or a historical monument, and then there are symbols that belong to the world of literature. Great symbolism in literature requires enormous intelligence and creativity on the part of author. Literary symbols allow tellers of tales to impart information without rehashing a long explanation or description of something.