For Nichiren, the Lotus Sūtra alone fully revealed the inherence of the buddha realm in all nine realms of unenlightened beings: By chanting its title, Namu Myōhō-renge-kyō, which instantiates the wisdom of all buddhas, even the most deluded person, he said, can manifest the buddha realm directly. Nichiren likened this to fire being produced by a stone taken from beneath the depths of water or a lamp illuminating a place that has been dark for millions of years.

Ichinen sanzen is a complex and challenging concept, and in his doctrinal instruction, Nichiren frequently concentrated on one of its key component principles: the mutual inclusion of the ten dharma realms (jikkai gogu). Traditional Buddhist cosmology divides saṃsāra or the realm of rebirth for unenlightened beings into a hierarchy of six paths: hell dwellers, hungry ghosts (preta), animals, demigods (asura), humans, and gods (deva). Above these, Tendai doctrine places four more realms characterized by ascending levels of awakening: the two realms of the śrāvakas and pratyekabuddhas, who cultivate the aims of detachment and cessation of desire set forth in the so-called Hinayāna teachings, aiming for the goal of Nirvāṇa; bodhisattvas, who strive for the liberation of all beings; and fully realized buddhas. In contrast to the buddha realm, which represents enlightenment, the other nine realms represent various levels of delusion, or states not yet fully awakened. Being empty of fixed, independent existence, all ten interpenetrate, meaning that each realm contains all ten within itself. Specifically, this means that the Buddha and all living beings are not separate; the buddha realm does not exist apart from oneself. Nichiren explains this in simple terms: “As to where hell and the Buddha exist: some sūtras say that hell lies beneath the ground, while others say that the Buddha dwells in the west. But close investigation shows that both exist within our five-foot body. For hell is in the heart of a man who despises his father and makes light of his mother, just as flowers and fruit are already present within the lotus seed. What we call ‘buddha’ dwells in our mind, in the same way that stones contain fire and that jewels have value intrinsically.”

Nichiren saw the Lotus Sūtra as all-encompassing, containing the whole of Buddhist truth within itself. All other sūtras reveal but partial aspects of that truth. Or, in Tendai terminology, the Lotus Sūtra is “true,” while all other sūtras are “provisional.” What this meant for Nichiren in practical terms was that the Lotus Sūtra alone enables all persons without exception to become buddhas. Nichiren grounded this claim in the “three thousand realms in a single thought-moment” (ichinen sanzen) a principle first articulated by Zhiyi. … In essence, this principle means that at each moment the smallest phenomenon (“a single thought-moment”) and the entire cosmos (“three thousand realms”) mutually pervade and encompass one another. Where Zhiyi had introduced this idea only briefly, Nichiren developed it as the very foundation of his thought.

[Nichiren’s] earliest surviving essay, written when he was twenty-one, suggests that he already took the Lotus Sūtra to be the sole teaching of universal buddhahood; his subsequent studies enhanced and deepened this conviction. Throughout, he was guided by the words of the Nirvāṇa Sūtra — regarded in Tendai circles as a restatement of the Lotus — to “rely on the dharma and not on the person.” For Nichiren, this meant that one should rely on the sūtras rather than the works of later commentators or the opinions of contemporary teachers, however eminent. And among the sūtras, one should rely above all on the Lotus, which is complete and final, and not others, which are incomplete and provisional. It is essential to bear in mind that for Nichiren, as for many of his contemporaries, the sūtras were literally the Buddha’s words; the stages of his fifty-year teaching career as mapped out in the Tendai doctrinal classification system represented historical truth; and the ranking of particular scriptures in the Tendai hierarchy of teachings directly mirrored their degree of salvific power.

The Japanese Buddhist teacher Nichiren (1222-1282), arguably the Lotus Sūtra’s most famous interpreter, lived and taught in a historical and cultural milieu quite different from that of the sūtra’s original compilers. As Buddhism spread through the Sinitic world, the Lotus had come to be widely revered as Śākyamuni Buddha’s highest and final teaching, and Nichiren asserted that only this sūtra represented his complete message. Like his contemporaries, Nichiren believed he was living in the age of the Final Dharma (J. mappō), a degenerate era when people are burdened by heavy karmic hindrances and liberation is difficult to achieve. Now in this evil era, he claimed, only the Lotus Sūtra leads to buddhahood; other teachings had lost their efficacy and must be set aside. Nichiren taught a form of Lotus practice accessible to all, regardless of social class or education: chanting the sūtra’s daimoku, or title, in the formula Namu Myōhō-renge-kyō. By chanting the daimoku with faith in the Lotus Sūtra, he said, one could realize buddhahood in this very lifetime. And, as faith in the Lotus Sūtra spread, the ideal buddha land would be realized in the present world.