The Buddha tells us that the were three turnings of the wheel of Dharma. In other words, that he gave his teachings in three different ways so that he could help free all beings from their suffering no matter what their experience or background. The first turning is made up of the earliest teachings of the Buddha that are preserved in the Pali Cannon and the other most ancient texts. Like a doctor diagnosing an illness, the first teachings the Buddha gave after his great enlightenment spelled out the cause of suffering and what to do about it in clear unambiguous terms. The Four Noble Truths he expounded tell us that suffering is caused by craving and attachment, and that the way to end that craving is to follow the Eightfold Noble Path he laid out. He told his followers that if they behaved with ethics and compassion, meditated diligently, and cultivated wisdom based on his teachings, they could free themselves from all suffering and achieve the ultimate release of nirvana. In these teachings, suffering is the disease, craving is the cause, and the Eightfold Path of ethical behavior, meditation and wisdom is the cure.
Even though the Buddha often warned his followers not to cling to his teachings, many people found them so profound and so helpful that they did exactly that. In the second turning, the Buddha did something unprecedented in the history of world religion. He dropped a bombshell that blew apart that clinging and along with it everything else many of the followers of his earliest teachings believed. In the Diamond Sutra, the Buddha tells us the he really has nothing at all to teach and that anyone who says he does slanders him. In the Heart Sutra, we are explicitly told that there is no suffering, no cause of suffering, no end of suffering and no noble path to lead from suffering. Everything, absolutely everything, is empty. Yet at the same time, emptiness itself is in separable from all the forms and appearances we perceive.
It is pretty obvious that the radical wisdom of the second turning is, as the sutras often say, “difficult, extremely difficult to understand,” and it left a lot of people amazed and confused. The sutras even tell us that when some of the Buddha’s followers first heard those teaching they fell down, vomited blood and died. Inevitably, some mistook those new teachings for some kind of shocking rejection of the older ones, while others fell victim to a kind of nihilism, reasoning that if everything is empty then nothing really matters and they are free to do what ever they please regardless of the consequences for others.
The third turning of the wheel sought to rectify such mistaken beliefs and provide more guidance to those who seemed to have had their feet cut out from under them by the great emptiness teachings of the second turning. The first step was to explain the apparent contradictions between the first turning of the wheel and the second. The title of the Samdhinirmocana Sutra actually means something like “the sutra revealing the hidden intent of the Buddha’s teachings,” and it in it he tells us that words are just “conventional designations” that he uses to help free us from suffering, and that no matter how different they seem all the teachings are of “one taste.” Like a good doctor, the Buddha was just giving different medicines to different patients depending on their individual needs. The teachings of the third turning go on to give more explicit guidance to practitioners by painting a profound picture of the way the conscious and subconscious mind operate and of the inconceivable ultimate, the buddha nature, that is their source.