Explain in detail:
The history and inheritance of the secret law predates Buddhism. The secret method existed before the birth of Sakyamuni Buddha. It belongs to an inheritance system of ancient Hinduism. In ancient India, the upper class inherited the secret law, so it was not introduced to the people, and the social structure at that time did not allow it. The secret method pays attention to the convenient method, and some methods used in the process of practicing the secret method are unacceptable to people in traditional society. So most people call it the secret method or the secret method because they can't understand it. In India, the secret law has existed since ancient times, but it has never been made public. People who practice the secret method are limited to a very small number of practitioners, and these practitioners often have no fixed place to live, and the outside world can't identify them. In the streets of some ancient cities in India or caves in the Himalayas, there are still practitioners practicing the secret method, but unlike Tibet, the secret method has not been listed as the mainstream religious system in India, so the word [secret method] has become very strange in today's Hindu sectarian system. In Tibet, the secret method has not only been summarized into the Tibetan Buddhist system, but also been inherited and kept very intact, which has become the basic feature of Tibetan Buddhism today.