According to Zhiyi’s parsing, Chapters Two through Nine of the Lotus Sūtra comprise the main exposition of the “trace teaching,” or shakumon, the first fourteen chapters of the Lotus Sūtra. These chapters assert that followers of the two “Hinayāna” vehicles can achieve buddhahood. For the sūtra’s compilers, this message subsumed the entire Buddhist mainstream within its own teaching of the one buddha vehicle and extended the promise of buddhahood to a category of persons — śrāvakas and pratyekabuddhas — who had been excluded from that possibility in other Mahāyāna sūtras. In Nichiren’s day, however, the idea of the one vehicle, that buddhahood is in principle open to all, represented the mainstream interpretive position, and his own reading therefore has a somewhat different emphasis. For Nichiren, the sūtra’s assertion that even persons of the two vehicles can become buddhas pointed to the mutual possession of the ten realms and the three thousand realms in a single thought-moment, without which any talk of buddhahood for anyone, even those following the bodhisattva path, can be no more than an abstraction. The revelation of this universal ground, he said, especially in the “Skillful Means” chapter, constitutes the heart of the shakumon portion of the Lotus. Nonetheless, he regarded Chapter Two through Chapter Nine, the main exposition section, as having been preached primarily for the benefit of persons during the Buddha’s lifetime. The remaining chapters, Chapter Ten through Chapter Fourteen, which constituted the remainder of the trace teaching, he saw as explicitly directed toward those who embrace the Lotus after the Buddha’s passing, and therefore, as having great relevance for himself and his followers.

Unlike Saichō, … Nichiren did not ground his own argument that all can attain buddhahood in claims for universal suchness, a term that occurs only rarely in his writings but, rather, in the mutual inclusion of the ten realms. This doctrine also renders irrelevant Hossō and Kegon claims that the Lotus Sūtra should be ranked below the Explanation of the Intention or Flower Garland sūtras because the parable of the wealthy man and his impoverished son, on which the Tendai hierarchy of Buddhist teachings is based, was spoken by śrāvakas. Nichiren wrote, “The four śrāvakas expressed their understanding, saying, ‘The most magnificent jewels have been obtained without being sought or awaited.’ They represent the śrāvaka realm within ourselves.” Central to Nichiren’s understanding was the idea that, because the ten realms are mutually inclusive, if beings of one realm can attain buddhahood, so can those of any other. In his reading, the initial chapters of the Lotus Sūtra open buddhahood not merely to previously exduded śrāvakas, but to all beings.

[A]fter Zhiyi’s time, through the efforts especially of Zhanran and the Korean scholar-monk Chegwan, the Tiantai school gradually developed a model that divides the Buddha’s teaching career into five periods that span fifty years. According to this model, the Buddha began by preaching the Flower Garland Sūtra (Avatamsaka Sūtra), a highly advanced doctrine directed solely to bodhisattvas. None of the śrāvakas in the assembly could understand it and were struck dumb, just as the impoverished son was terrified when first forcibly approached by his father’s attendants. Seeing that the Flower Garland teaching was beyond his auditors’ capacity, the Buddha then backtracked and for twenty years preached the āgamas, … emphasizing the four noble truths, the twelve-linked chain of dependent origination, and the goal of nirvāṇa — that is, the teachings sometimes disparaged as the “Hinayāna.” This period corresponds to the wealthy man hiring his son to sweep manure for twenty years. In the third period, seeing that his followers were maturing, the Buddha preached the vaipulya or introductory Mahāyāna teachings such as the Vimalakirti Sūtra, which criticize the one-sided emphasis on emptiness and detachment found in the āgamas and instead extol the way of the bodhisattva. This corresponds to the son having “free access to his father’s house” yet still living in his own humble quarters. In the fourth period, the Buddha preached the prajn͂ā or wisdom teachings, which integrate all of his teachings up to that point in the two discernments of emptiness and wisdom by which bodhisattvas both uproot attachment and act compassionately in the world. This corresponds to the wealthy man entrusting the care of his fortune to his impoverished son. Then finally, in the fifth period, during the last eight years of his life, the Buddha set aside the coarse and incomplete provisional teachings of the preceding four periods and preached the perfect teaching that opens buddhahood to all. This teaching is represented by the Lotus Sūtra, and — in the Tiantai reading — restated in the Nirvāṇa Sūtra, said to have been preached just before the Buddha’s passing. This corresponds to the father, now approaching death, publicly acknowledging his son and bequeathing all of his wealth to him. In this way, the parable of the wealthy householder provided a basis for grasping the entirety of the Buddha’s teachings as integrated into a single, comprehensive chronological and soteriological agenda, by which he sought to gradually cultivate his followers’ capacity until they were mature enough to receive and accept the message of the one buddha vehicle.