The Soka Gakkai Dictionary of Buddhism
three thousand realms in a single moment of life[一念三千] (Jpn ichi- nen-sanzen )
Also, the principle of a single moment of life comprising three thousand realms. "A single moment of life" (ichinen) is also translated as one mind, one thought, or one thought-moment. A philosophical system established by T'ient'ai (538-597) in his Great Concentration and Insight on the basis of the phrase "the true aspect of all phenomena" from the "Expedient Means" (second) chapter of the Lotus Sutra. The three thousand realms, or the entire phenomenal world, exist in a single moment of life. The number three thousand here comes from the following calculation: 10 (Ten Worlds) 10 (Ten Worlds) 10 (ten factors) 3 (three realms of existence). Life at any moment manifests one of the Ten Worlds. Each of these worlds possesses the potential for all ten within itself, and this "mutual possession," or mutual inclusion, of the Ten Worlds is represented as 102, or a hundred, possible worlds. Each of these hundred worlds possesses the ten factors, making one thousand factors or potentials, and these operate within each of the three realms of existence, thus making three thousand realms.
The theoretical teaching (first half) of the Lotus Sutra expounds the ten factors of life. It also sets forth the attainment of Buddhahood by persons of the two vehicles (voice-hearers and cause-awakened ones), which signifies the mutual possession of the Ten Worlds. The essential teaching (latter half) of the sutra reveals the true cause (the eternal nine worlds), the true effect (eternal Buddhahood), and the true land (the eternal land or realm of the environment). T'ient'ai unified all these concepts in one system, three thousand realms in a single moment of life.
Volume five of Great Concentration and Insight reads: "Life at each moment is endowed with the Ten Worlds. At the same time, each of the Ten Worlds is endowed with all Ten Worlds, so that an entity of life actually possesses one hundred worlds. Each of these worlds in turn possesses thirty realms, which means that in the one hundred worlds there are three thousand realms. The three thousand realms of existence are all possessed by life in a single moment. If there is no life, that is the end of the matter. But if there is the slightest bit of life, it contains all the three thousand realms.... This is what we mean when we speak of the 'region of the unfathomable.'"
"Life at each moment" means life as an indivisible whole that includes body and mind, cause and effect, and sentient and insentient things. A single moment of life is endowed, as stated above, with the three thousand realms. The relationship of these two elements is not such that one precedes the other, or that they are simultaneous in the sense that one is included in the other. Actually they are non-dual or, as T'ient'ai put it, "two [in phenomena] but not two [in essence]." The provisional teachings stated that all phenomena arise from the mind, or that they are subordinate to the mind. The Lotus Sutra clarifies that the true aspect is inseparable from all phenomena, and that all phenomena, just as they are, are in themselves the true aspect. When T'ient'ai stated, "The three thousand realms of existence are all possessed by life in a single moment.... But if there is the slightest bit of life, it contains all the three thousand realms," he is referring to the non-duality of "a single moment of life" and the "three thousand realms."
"The three thousand realms in a single moment of life" is classified into two as the theoretical principle and the actual embodiment of this principle. These are respectively termed the "theoretical three thousand realms in a single moment of life" and the "actual three thousand realms in a single moment of life." The theoretical principle is based on the theoretical teaching of the Lotus Sutra, which expounds the equality of Buddhahood and the nine worlds. Both, it points out, are manifestations of the true aspect. The theoretical teaching also reveals the mutual possession of the Ten Worlds based on the principle that persons of the two vehicles, who were denied Buddhahood in the provisional teachings, also possess innate Buddhahood and can attain it. Strictly speaking, however, the theoretical teaching reveals only the hundred worlds and, multiplying by the ten factors of life, the thousand factors, and does not reveal their eternal nature. Only when supported by the essential teaching (the latter half) of the Lotus Sutra, can the theoretical teaching be said to expound theoretically, as a possibility, the three thousand realms in a single moment of life.
On the other hand, the essential teaching reveals Shakyamuni's enlightenment in the remote past (the true effect, eternal Buddhahood), the eternal life of his disciples, the Bodhisattvas of the Earth (the true cause, the eternal nine worlds), and the eternity of the saha world (the true land). These explain the eternal Ten Worlds and the eternal three realms of existence, and thus "the actual three thousand realms in a single moment of life."
Despite its comprehensive view, the essential teaching does not go on to reveal the practice that enables one to embody directly this principle of three thousand realms in a single moment of life. Though the sutra says, "If there are those who hear the Law, then not a one will fail to attain Buddhahood," it does not identify what the Law is. That is why Nichiren (1222-1282) defined the entire Lotus Sutra—both the theoretical and the essential teachings—as representing "the theoretical three thousand realms in a single moment of life."
In contrast, Nichiren embodied his life embracing the three thousand realms in a single moment, or the life of Nam-myoho-renge-kyo, in the mandala known as the Gohonzon and established the practice for attaining Buddhahood. That practice is to chant Nam-myoho-renge-kyo with faith in the Gohonzon. In Nichiren's teaching, this is the practice for "observing the mind," i.e., observing one's own mind and seeing Buddhahood in it. For this reason, his teaching is summarized in the phrase "embracing the Gohonzon is in itself observing one's mind" or "embracing the Gohonzon is in itself attaining Buddhahood."
He states in a 1273 letter known as Reply to Kyo'o, "I, Nichiren, have inscribed my life in sumi ink, so believe in the Gohonzon with your whole heart. The Buddha's will is the Lotus Sutra, but the soul of Nichiren is nothing other than Nam-myoho-renge-kyo" (412), and in his 1273 treatise The Object of Devotion for Observing the Mind: "Showing profound compassion for those unable to comprehend the gem of the doctrine of three thousand realms in a single moment of life, the Buddha wrapped it within the five characters [of Myoho-renge-kyo], with which he then adorned the necks of the ignorant people of the latter age" (376).
Nichikan (1665-1726), the twenty-sixth chief priest of Taiseki-ji temple, interpreted the above passage of volume five of Great Concentration and Insight from the viewpoint of Nichiren's teaching. Nichikan defined "life at each moment" as the life of the eternal Buddha, or Nam-myoho-renge-kyo, which is inscribed down the center of the Gohonzon; he further interpreted "endowed with the Ten Worlds" as the Buddhas, bodhisattvas, and other figures inscribed on both sides of Nam-myoho-renge-kyo in the Gohonzon. These represent the principles of the mutual possession of the Ten Worlds, the hundred worlds and the thousand factors, and the three thousand realms. According to Nichikan, the sentence "The three thousand realms of existence are all possessed by life in a single moment" refers to the "region of the unfathomable," which he interprets as the object of devotion that embodies the principle of three thousand realms in a single moment of life. This is not to be viewed simply as an external object but as something that exists in the life of a person with faith in the object of devotion. Without faith, the object of devotion endowed with the three thousand realms does not exist within one's life. This, Nichikan stated, is the ultimate meaning of T'ient'ai's doctrine.