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).
"In these studies of Kabbalah, we need to be practical; there are authors who write marvels, but when one looks at them, one realizes that they have not lived what they have written; they did not experience it in themselves, and that is why they are mistaken. I understand that one must write what one has directly experienced by oneself. I have proceeded in this way for my part."