The doctrine of the “mutual possession of the ten realms” is not explained in any sūtras expounded during forty years or so of the Buddha’s preaching except in the Lotus Sūtra. Since the “mutual possession of the ten realms” doctrine is not preached, believers of those sūtras do not know about the realm of Buddhas inherent in their minds.

Unaware of the realm of Buddhas in their minds, they do not know of other Buddhas outside of their minds either. Namely, practicers of expedient sūtras preached in the pre-Lotus period of forty years or so do not know of Buddhas. Even if they see Buddhas, they merely see Buddhas in other worlds, not real Buddhas.

Practicers of the two teachings, śrāvaka and pratyekabuddha, are unaware of the Buddha within their own minds, so they cannot become Buddhas. Bodhisattvas of the pre-Lotus sūtras, unaware of the “mutual possession of the ten realms,” themselves deny the attainment of Buddhahood by practicers of śrāvaka and pratyekabuddha teachings. Thus, they are unable to fulfill their vow of saving all people. These bodhisattvas do not see the Buddha. Likewise, ignorant people do not know the “mutual possession of the ten realms,” so the Buddha realm inherent in them is not revealed. As a result, the Buddha of Infinite Life will not come to welcome them at the last moment of life, and Buddhas will not come to help them upon request. They are like the blind who cannot see their own shadow.

Now in the Lotus Sūtra, it was clarified that the Buddha realm is inherently possessed by even those in the unenlightened nine realms, enabling those who had listened to the expedient pre-Lotus sūtras–bodhisattvas, Two Vehicles (śrāvaka and pratyekabuddha ), and those in the six realms of illusion–all to see for the first time the Buddha realm in themselves. It was the first time that those people were able to become true Buddhas, true bodhisattvas and true śrāvaka and pratyekabuddha. It was the first time that bodhisattvas and śrāvaka and pratyekabuddha attained Buddhahood and ignorant people were able to be reborn in the Pure Land. Regardless, during or after the lifetime of the Buddha, the true, trustworthy teacher (“good friend”) of all the people is the Lotus Sūtra. Tendai scholars in general assert that one can achieve enlightenment through pre-Lotus sūtras, but I, Nichiren, do not accept it. Having no time to discuss this thoroughly in this book, I merely mention it here briefly. I hope to discuss it in detail someday.

Shugo Kokka-ron, Treatise on Protecting the Nation, Writings of Nichiren Shōnin, Doctrine 1, Page 60-61