Popularly called "the Wheel of Samsara," the Bhavachakra is one of the most important symbols in Buddhism, being an illustration of everything that exists and how existence functions. While the superficial, public-level meanings are fairly well-known (such as the three poisons, the twelve nidanas, the six realms), few know that the actual purpose of the symbol is very deep, revealing the inner workings of our mind, and thereby illustrates the source of suffering (samsara) or liberation from suffering (nirvana).
"We should not mistake the Truth with opinions. Many think that the Truth is this or that, or that the Truth is within this or that book, or within this or that belief or idea, etc. Whosoever wants to experience the Truth should not mistake beliefs, ideas, opinions and theories with that which is the Truth. We must experience the Truth in a direct, practical and real manner; this is only possible in the stillness and silence of the mind, and this is achieved by means of meditation."