The Chinese symbol known as the yin-yang.
What are symbols? When analyzing literature I often focus on the symbols found throughout specific works. But what are symbols? A symbol is an image. But not any image can be a symbol. In a novel, a symbol is an image that occurs throughout the work at important scenes, important events, with specific characters, and so on. The reason writers use symbols in their works, and this sometimes happens unconsciously as the subconscious rises during writing and is molded to coherent, poetic words through editing, is because of the notion that images express so much more than words. The symbols that are used in literature are images that hold meaning independently, meaning that we can all understand by seeing it or visualizing it.
The beauty of a symbol is that it is an image that regardless of its origins, can be applied to a wide variety of notions, spiritual beliefs, and so on. A symbol, such as the yin yang, can be used to refer to almost anything and still holds onto its original meaning. The yin yang, regardless of what your mind applies it to, will always represent duality, meaning two. These are the most powerful symbols, those that can be used for anything without losing their meaning and purpose.
The Hindu swastika.
However, these powerful symbols can be misused and they have been. The meaning of a symbol is dependent on the masses. Meaning that if many people understand an image to mean the same thing, then it becomes a symbol. Because of this there is risk of manipulation. The most famous example of abuse and misuse of a symbol is the swastika. Adolf Hitler took the Hindu symbol and turned it into something corrupt and malicious. Though the swastika is known as being a Hindu symbol it was (and probably still is) used by other spiritual/religious practices.
Images, like words and sound, affect our minds; which is why symbols are widely used in spiritual practices. What symbols do is they speak to our consciousness; specifically to the subconscious and through the eyes, using images, the knowledge within comes forth to the conscious mind, where it is understood and/or analyzed.