The beginnings of Nichiren’s eventual thinking concerning the daimoku are, however, already present in his Ichidai shōgyō taii (The cardinal meaning of the sacred teachings of the Buddha’s lifetime), written in 1258, which declares the Lotus Sūtra to be the Buddha’s ultimate teaching and the purpose of his advent in this world. In this work, Nichiren identifies the five characters of the daimoku, the “Wonderful Dharma,” with the “three thousand realms in one thought-moment” (ichinen sanzen), an identification that would be central to his later writings. The Ichidai shōgyō taii also foreshadows the importance Nichiren would place on the concept of the “three thousand realms in one thought-moment” as the foundation of his mature thought. Unlike the majority of medieval Tendai kuden texts, Nichiren took as his doctrinal basis not the threefold contemplation in a single mind, but the three thousand realms in a single thought-moment. While both concepts express the idea of a perfectly interpenetrating universe in which all dharmas simultaneously encompass one another, the “three thousand realms in one thought-moment” explicitly includes two component principles that Nichiren would draw upon in developing his thought. One is the mutual inclusion of the ten dharma realms (jikkai gogu), which Nichiren used to focus more diffuse notions of nonduality on the mutual encompassing of the Buddha realm and the nine realms of unenlightened beings. The other is the concept of the land (kokudo seken), which is nondual with and inseparable from the beings who inhabit it. This concept would be important to Nichiren for two reasons. First, it underlies his claim that the land itself can manifest Buddhahood, that is, that the pure land can be realized in the present world. Second, its implication that insentient forms can manifest Buddhahood provided the doctrinal basis for his use of a mandala as a honzon or object of worship. (Page 248-249)

The concept of the “three thousand realms in a single thought-moment” is not, however, merely an analysis of the structure of reality. It is the “realm of the inconceivable” to be discerned in meditation by the practitioner, who in so doing realizes one’s own identity with the totality of all that is. Kanno Hiroshi, in an essay on ichinen sanzen, lists five soteriological implications of this concept.

1. By virtue of the ten suchnesses, which constitute “the true aspect of the dharmas,” all beings in the hierarchy of the ten dharma realms, from hell-dwellers at the bottom to Buddhas at the top, are shown to have a common ontological structure, upon which the mutual inclusion of the ten realms can be asserted. Thus, the ichinen sanzen concept structurally clarifies the basis upon which deluded beings can realize Buddhahood. Specifically, because the Buddha realm is inherent in the human realm, ordinary worldlings can potentially become Buddhas.
2. As a corollary, the ontological equality of all beings is established, whatever their place in the hierarchy of the ten dharma realms.
3. Just as the Buddha realm is contained even in the hell realm, so the hell realm is contained even in the realm of Buddha. This undergirds the claim that the Tathāgata still possesses the nature of evil innately and thus clarifies the basis of the Buddha’s compassion, upon which his salvation of evil beings can become reality.
4. The subjective individual and the objective dharma realm are shown to be nondual; hell-dwellers live in hells, Buddhas in Buddha lands, and so on. Thus, potentially, the individual’s realization of Buddhahood can transform the outer world. As will be noted in chapter 6, this implication of the ichinen sanzen concept undergoes particular development in the teaching of Nichiren.
5. All existential possibilities, from the utmost suffering of the hells to the Buddha’s liberation, are implicit in the present thought-moment of the ordinary person; thus, all potential is located within the individual. (Page 181)