The Legend of the Origins of The Esoteric Teachings
According to Shingon legend, Vajrasattva, after having been initiated by Mahavairocana into the deepest mysteries of Buddhism, hid himself within an iron tower in southern India. There the Bodhisattva concealed himself for centuries, until Nagarjuna opened the Iron Tower and, according to one version of this legend, received from Vajrasattva the two major sutras of Shingon Buddhism, the Mahavairocana Sutra and the Vajrasekhara Sutra.
Herein lies the fundamental teaching and practice of Shingon Esoteric Buddhism. Our bodies, speech, and minds in their present state become the body, speech, and mind of the Buddha, and we thereby become a buddha. This is the realm of the deep but lofty enlightenment that is unique to Shingon Buddhism. </poem>