The sutras expounded prior to the Lotus Sutra cannot lead to Buddhahood because they are provisional and expedient teachings that separate reality and wisdom. The Lotus Sutra, however, unites the two as a single entity. The sutra says that the Buddhas open the door of Buddha wisdom to all living beings, show it, cause them to awaken to it, and induce them to enter its path. By realizing this Buddha wisdom, one attains Buddhahood.
This inner enlightenment of the Buddha is far beyond the understanding of Voicehearers and Pratyekabuddhas. This is why the “Expedient Means” chapter goes on to say, “Not one of the voicehearers or pratyekabuddhas is able to comprehend it.”
What then are these two elements of reality and wisdom? They are simply the five characters of Nam myoho renge kyo. Shakyamuni Buddha called forth the Bodhisattvas of the Earth and entrusted to them these five characters that constitute the essence of the sutra. This is the teaching that was transferred to the bodhisattvas who had been the disciples of the Buddha since the remote past.
The sutra states, “Those persons who had heard the Law dwelled here and there in various Buddha lands, constantly reborn in company with their teachers,” and “If one stays close to the teachers of the Law, one will speedily gain the bodhisattva way. “In the Latter Day of the Law, there is no Treasure Tower other than the figures of the men and women who embrace the Lotus Sutra. It follows therefore, that those who chant Nam Myoho Renge Kyo, irrespective of social status, are themselves the Treasure Tower and likewise themselves are Taho Buddha.”
This is not just a literary device. Nichiren means that physically we are the Treasure Tower of Nam Myoho Renge Kyo and participate in the Ceremony in the Air. In the Ongi Kuden, he makes this clear in a passage I found very moving:
'Treasure' indicates the five components [earth, water, fire, wind, and ku] and 'Tower' their temporary union. To see that the five components in their temporary union are the five characters of the Mystic Law is to "behold the Treasure Tower." Now Nichiren and his disciples who chant Nam-myoho-renge-kyo behold the Treasure Tower. .. The sutra states, "All four sides [of the tower] emitted a fragrance of tamalappatra sandalwood that pervaded the whole world." The four faces of the Treasure Tower represent the sufferings of birth, old age, sickness, and death. These four aspects, or noble truths of life, dignify our individual lives. By chanting the Daimoku, through these four aspects, we send forth the fragrance of the four virtues, self, eternity, purity, and happiness, from our lives. 'Nam' indicates the perfection [paramita] of happiness, 'Myoho' is the perfection of self, 'Renge' is the perfection of purity and 'Kyo' is the perfection of eternity. Thus, we adorn the Treasure Tower of our bodies with the four aspects of birth, old age, sickness, and death. When we chant Nam Myoho Renge Kyo in birth, old age, sickness, and death, the fragrance of the four virtues emerges.