Buddhism, with its manifold jeweled nets of cause and effect and co-dependent arisings, naturally has various articulations of the concept of buddhanature. Shinnyo-en traces its idea of buddhanature through various threads of Mahayana Buddhism, which comprises a large number of sutras and commentaries. The idea that anyone has the potential to become a buddha is a prominent theme found amongst the schools of Mahayana Buddhism. As it is expressed in a key phrase found in the Mahayana Mahaparinirvana Sutra, often referred to as the Nirvana Sutra: "All sentient beings have a buddha-nature."
In Sanskrit, the language in which the Mahaparinirvana Sutra was most likely first written, the word for buddhanature is buddha-dhatu. "Dhatu" conveys a sense of essence or quality, indicating that "buddhaness" is the true essence or quality of all beings, and as a result, all beings possess the possibility of becoming a buddha. It is a very optimistic approach to the nature of humanity. (Read more here)
