The Lotus Sūtra is named the “Wonderful Dharma” because it expounds that each of the Ten Realms mutually possesses the characteristics of the other nine realms, which means that all of the Ten Realms are equipped with the realm of Buddhas. In the mutual possession of the Ten Realms, each realm includes the other nine realms. As a result the Ten Realms have other Ten Realms, consisting of the hundred realms of all phenomena. The second fascicle of the Profound Meaning of the Lotus Sūtra says, “The one realm of all phenomena equipped with the other nine realms of all phenomena means the hundred realms of all phenomena.” It is not only in the Lotus Sūtra that the Ten Realms are mentioned. The cause and effect of the Ten Realms is revealed in the pre-Lotus sūtras as well. The reason why the Lotus Sūtra is regarded as the Wonderful Dharma is because the sūtra expounds the mutual possession of the cause and effect of the Ten Realms.

Ichidai Shōgyō Tai-I, Outline of All the Holy Teachings of the Buddha, Writings of Nichiren Shōnin, Doctrine 3, Page 86