Ichinen Sanzen established by Grand Master T’ien-tai is called Ichinen Sanzen of Ri or Ichinen Sanzen of the theoretical section of the Lotus Sutra. On the other hand, Ichinen Sanzen understood by Nichiren Shōnin is called Ichinen Sanzen of Ji or Ichinen Sanzen of essential section of the Lotus Sutra. … [T]he core of Nichiren Shōnin’s religion is Ichinen Sanzen, especially the mutual possession of the ten realms. T’ien-tai’s Ichinen Sanzen is focused on the ten suchnesses of Chapter 2, Expedients, of the Lotus Sutra. In Nichiren Shōnin’s understanding of Ichinen Sanzen, it is most important that nine realms possess the realm of Buddha and also that the realm of Buddha possesses the other nine realms. Without this mutual possession between the realm of Buddha and the nine realms, Sokushin Jōbutsu (attaining Buddhahood with one’s current body) and Juji Jōbutsu (attaining Buddhahood by upholding the Dharma) would not be possible.
