In the essential section of the Lotus Sūtra, it was revealed that the Buddha had attained perfect enlightenment in the eternal past, making it untenable to assert that He attained Buddhahood for the first time in this world. Thus the Eternal Buddha doctrine destroyed the Buddhahood resulting from the Four Teachings (all Buddhist scriptures other than the essential section of the Lotus Sūtra). As the Buddhahood resulting from the Four Teachings became untenable, the way leading to Buddhahood shown in those Four Teachings proved to be invalid. Thus the Ten Realm doctrine preached in the pre-Lotus and the theoretical section of the Lotus was destroyed and the doctrine of causal relationship among the eternal Ten Realms was established in the essential section of the Lotus Sūtra. This is the doctrine of the “true cause and true result.” In this relationship the Nine Realms are all included in the realm of the Eternal Buddha, and the realm of the Buddha is in each of the eternal Nine Realms. This is truly the “mutually-possessed characteristics of the Ten Realms,” “100 realms and 1,000 aspects of existence” and “3,000 in one thought.”

Kaimoku-shō, Open Your Eyes to the Lotus Teaching, Writings of Nichiren Shōnin, Doctrine 2, Page 48-49