The teaching of the “3,000 in one thought” is based on the “mutually-possessed characteristics of the Ten Realms” meaning that each of the Ten Realms has the characteristics of the other nine. Ignorant of the Ten Realms, the Hossō and Sanron Sects established the Eight Realm theology, missing the realm of bodhisattvas and that of Buddhas. How can they know of the mutually-possessed characteristics of the Ten Realms? The Kusha, Jōjitsu, and Ritsu Sects, based on the Āgama sūtras, preach only Six Realms, ignoring the top four of the ten. They insist on the existence of the one and only Buddha in the worlds throughout the universe, denying the existence of His manifestation in each of these worlds. It is only natural that they leave out the concept of every living being having the Buddha-nature. They do not recognize the possession of the Buddha-nature by man. Nevertheless, the Ritsu and Jōjitsu Sects today speak of the existence of Buddhas in various worlds throughout the universe or of the Buddha-nature in man. It must have been that scholars after the death of the Buddha plagiarized the Mahāyāna doctrines to the advantage of their own schools.

Kaimoku-shō, Open Your Eyes to the Lotus Teaching, Writings of Nichiren Shōnin, Doctrine 2, Page 35