Although the very notion of a “seed” tends to suggest a gradual process of growth and maturation, in Nichiren’s thought, because “original cause” and “original effect” are simultaneous, the “process” of sowing, maturing, and harvesting also occurs simultaneously. This is called, in the terminology of Nichirenshū doctrine, “the seed being simultaneously [the harvest of] liberation” (shu soku datsu). Nichiren explains this idea in readily accessible terms to a lay follower:

The mahā-mandārava flowers in heaven and the cherry blossoms of the human world are both splendid flowers, but the Buddha did not choose them to represent the Lotus Sūtra. There is a reason why, from among all flowers, he chose this [lotus] flower to represent the sūtra. Some flowers first bloom and then produce fruit, while others bear fruit before flowers. Some bear only one blossom but many fruit, others send forth many blossoms but only one fruit, while others produce fruit without flowering. In the case of the lotus, however, flowers and fruit appear at the same time. The merit of all [other] sūtras is uncertain, because they teach that one must first plant good roots and [only] afterward become a Buddha. But in the case of the Lotus Sūtra, when one takes it in one’s hand, that hand at once becomes Buddha, and when one chants it with one’s mouth, that mouth is precisely Buddha. It is like the moon being reflected in the water the moment it appears above the eastern mountains, or like a sound and its echo occurring simultaneously.(Page 271)

Nichiren accepted the received Mahāyāna view that “all sentient beings have the Buddha nature,” as well as Tendai ideas about the Buddhahood of insentient beings, but did not himself develop a particular theory of Buddha nature. Rather, as a number of postwar Nichirenshū scholars have pointed out, he emphasized the daimoku as the “seed” of Buddhahood. While ideas about the “Buddha-seed” (busshu) have a long and varied history, Nichiren’s concept draws explicitly on Chih-i’s Fa-hua hsüan-i, which describes the Buddha as leading the beings to enlightenment by first sowing the seed of enlightenment by preaching them the Lotus Sūtra, then bringing it to maturity, and finally reaping the harvest of liberation, a process transpiring over successive lifetimes. Nichiren makes explicit that it is always the Lotus Sūtra that sows the initial seed. While people in the True and Semblance Dharma ages might have progressed spiritually and even reached the maturity of full enlightenment through other teachings, this was only because they had first received the seed of Buddhahood by hearing the Lotus Sūtra in prior lifetimes. This idea also occurs in certain medieval Tendai texts attributed to Saichō, and it is possible that Nichiren’s emphasis on the seed of Buddhahood reflects more general developments within the broader field of contemporary Lotus Sūtra interpretation. However, Nichiren’s reading is distinctive in that it identifies the seed of Buddhahood as the daimoku (“All Buddhas of the three time periods and ten directions in variably attain Buddhahood with the seed of the five characters Myōhōrenge-kyō”) or as the “three thousand realms in one thought-moment.” Nichiren also connects the notion of the seed of Buddhahood specifically to the Final Dharma age. People in this age, he claims, have never before received this seed in prior lifetimes; they are people “originally without good [roots] ” (honmi uzen):

At this time, Namu-Myōhō-Renge-Kyō of the “Fathoming the Lifespan” chapter, the heart of the teaching of origin, should be planted as the seed [of Buddhahood in the minds] of the two kinds of persons who inhabit this defiled and evil age–those who commit the [five] perverse [offenses] and those who slander [the True Dharma].

(Page 270-271)

[T]he “contemplation of the mind” in Nichiren’s teaching is not the introspective meditation on the moment-to-moment activity of one’s (unenlightened) mind, but rather embracing the daimoku, which is said to embody the enlightenment of the eternal Buddha of the origin teaching, that is, the three thousand realms in a single thought-moment in actuality.

“Embracing” the daimoku has the aspects both of chanting and having the mind of faith (shinjin); for Nichiren, the two are inseparable. Faith is also all-inclusive: in the Final Dharma age, it substitutes for the three disciplines of precepts, meditation, and wisdom. “That ordinary worldlings born in the Final Dharma age can believe in the Lotus Sūtra is because the Buddha realm is inherent in the human realm.” Thus the “one thought-moment containing three thousand realms” is also the “single moment of belief and understanding.” In the moment of faith, the three thousand realms of the original Buddha and those of the ordinary worldling are one. This moment of faith corresponds to the stage of myōji-soku. Like that of many medieval Tendai texts, Nichiren’s thought focuses on realizing Buddhahood at the stage of verbal identity, which he understood as the stage of embracing the daimoku of the Lotus Sūtra and taking faith in it. (Page 270)

The practices carried out by the Buddha throughout his countless lifetimes (causes) and the resulting virtues of his enlightenment (effects) are contained in the daimoku and spontaneously accessed by the practitioner in the act of chanting. We can see this idea developing in a personal letter that Nichiren wrote the year before the Kanjin honzon shō:

This jewel of [the character] myō contains the merit of the Tathāgata Śākyamuni’s Pāramitā of giving (danbaramitsu), when in the past he fed his body to a starving tigress or [gave his life] to ransom a dove; the merit of his Pāramitā of keeping precepts, when, as King Śrutasoma, he would not tell a lie; the merit gained as the ascetic Forbearance, when he entrusted his person to King Kali; the merit gained when he was Prince Donor, the ascetic Shōjari, [etc.] He placed the merit of all his six perfections (rokudo) within the character myō. Thus, even though we persons of the evil, last age have not cultivated a single good, he confers upon us the merit of perfectly fulfilling the countless practices of the six perfections. This is the meaning [of the passage], “Now this threefold world / is all my domain. / The beings in it / are all my children.” We ordinary worldlings, fettered [by defilements], at once have merit equal to that of Śākyamuni, master of teachings, for we receive the entirety of his merit. The sūtra states, “[At the start I made a vow / to make all living beings] / equal to me, without any difference.” This passage means that those who take faith in the Lotus Sūtra are equal to Śākyamuni Commoners [i.e., the heirs chosen to succeed the emperors Yao and Shun] immediately achieved royal status. Just as commoners became kings in their present body, so ordinary worldlings can immediately become Buddhas. This is what is meant by the heart of [the doctrine of] three thousand realms in one thought-moment.