Śākyamuni Buddha gave the Original Gate discourse to his disciples two thousand five hundred years ago in India at a time when their understanding was ripe and they could awaken to the fullest implications of what they were being told. The ‘three thousand realms in a single thought-moment’ is the Tiantai way of expressing the contemplative insight that is implied by the Original Gate of the Lotus Sūtra. Therefore, it is called the seed of buddhahood. In other writings, particularly Treatise on Spiritual Contemplation and the Focus of Devotion (Kanjin Honzon-shō), Nichiren identifies this seed with the Odaimoku (Sacred Title) of the five characters of the Lotus Sūtra: myō, hō, ren, ge, and kyō. Nichiren sees the present age as the time in which to sow this seed of buddhahood. Because of this seed, buddhahood is something that is not only found in the past or the future but is a reality that can be sown in our lives in the present moment.

Kūkai’s understanding was that all beings are originally enlightened or awakened, and that they only have to realize their intrinsic unity with Mahāvairocana Buddha. This realization can come about through the practice of the three mysteries. He explains it as follows in his essay The Meaning of Becoming a Buddha in This Very Body.

On the basis of this meaning it says, “When empowered by the three mysteries, [Buddhahood] is quickly manifested.” “Empower” (lit., “add and hold”) expresses the great compassion of the Tathāgata and the faithful minds of sentient beings: the reflection of the Buddha sun appearing on the mind-water of sentient beings is called “adding” and the mind-water of the practitioner sensing the Buddha-sun is called “holding.” If the practitioner contemplates well on this guiding principle, through the intercorrespondence of his three mysteries [with those of the Tathögata] he will quickly manifest and realize in his present body the originally existent three bodies. Therefore it is said, “[Buddhahoodl is quickly manifested.” (Giebel 2004, p. 79)

The thought that all beings are originally enlightened and possessed of the three bodies of the Buddha and only need to take faith in the Eternal Buddha (whether understood as the Dharma-body Mahāvairocana Buddha or the Eternal Śākyamuni Buddha of the Lotus Sūtra) and express buddhahood through ritual practices utilizing mudrās, mantras, and the contemplation of mandala images would later be incorporated into Tendai Buddhism and then into Nichiren Buddhism. The result was that practices such as meditative cultivation of the mind in order to perceive the truth were believed to be surpassed by practices in which the original enlightenment made itself immediately manifest in concrete ritual practices that would transform the practitioner into a buddha. …

In regard to Nichiren specifically, [Jacqueline] Stone wrote:

Where Chih-i’s form of meditative discipline was that of “principle,” or introspective contemplation to perceive the truth aspect of reality in one’s mind, Nichiren’s was that of “actuality,” or the chanting of the daimoku, the title of the Lotus Sūtra, said to embody the reality of the Buddha’s enlightenment and the seed of Buddhahood.

Nichiren’s usage reflects the strong influence of esoteric Buddhism, in which ri refers to formless truth that is contemplated inwardly, and ji, to its expression in outwardly manifest practices involving concrete forms.(Stone 1999, pp. 68)