Although the Buddha provided the “hearers,” “private Buddhas,” and Bodhisattvas with three different ways, the essence of the three identities is Bodhisattvahood. Those who don’t realize this fact and hold on to their particular beliefs that they are either arhats (perfect ones) or “private Buddhas” (self-enlightened), are neither true arhats nor true “private Buddhas.” When he is teaching them, the Buddha regards them as being Bodhisattvas. They must be Bodhisattvas at heart even if they are “hearers” or “private Buddhas” in appearance. This is why the sutra says, “The Buddhas teach only Bodhisattvas.”

The studies conducted over so many centuries made possible a deeper understanding of the Lotus Sutra, and methodological standards for its interpretation were established. One example is called Kamon. It is a classification of the twenty-eight chapters into several sets for a systematic explanation of their meaning.

The major Kamon is the “Three Parts of Each of the Two Divisions of the Lotus Sutra” which was established by Great Master Chih-i. Most commentators since his time have accepted his guidelines. …

[T]he “Three Parts of Each of the Two Divisions of the Lotus Sutra” refers to the division of the Sutra into two main sections: the first half, consisting of Chapters One through Fourteen, and the second half, consisting of Chapters Fifteen through Twenty-eight. Kamon gives a detailed explanation of the reason for this division. The first half is named Shakumon, literally “imprinted gate.” Its main purpose is to teach how “hearers” and Pratyekabuddhas can attain Buddhahood in the One Vehicle. The second half is called Hommon, which means “Primal Gate” or “Primal Mystery.” This part reveals Sakyamuni to be the infinite, absolute Buddha, the Buddha who attained enlightenment in the remotest past but still leads living beings in the present. These two points are considered the fundamental ideas of the Lotus Sutra.

The Lesser Vehicle of the “Sravaka” and “Pratyekabuddha” drew a sharp line between this world of sufferings and the pure world of spirit. Its followers renounced worldly concerns, devoted their lives to religious austerities, and made every effort to attain absolute tranquility. This made for a two-dimensional world view, esteeming the pure world of spirit and devaluating the everyday world in which we live.

Bodhisattvas, on the other hand, saw the two worlds as one. They saw this world as the center stage for their religious practice, and preached that spiritual enlightenment must be realized in our life in this world. In short, the Bodhisattva’s mission to deliver people from suffering is to be accomplished in this world of sufferings.

[W]ords function only if commonly understood within a given society. If they are clearly understood, they bear objective meanings. This objectivity, however, is not absolute. It depends on conventional practices mutually agreed upon within a particular society. Something acceptable or commonly understood within one society may be neither acceptable nor understood in another society. Words, by themselves, cannot express the truth in full. If someone wants to expound the truth in words, his explanation will naturally have the characteristic of an expedient. The truth of enlightenment is beyond all our normal experience. There are no words to describe it. Therefore it can be expressed only partially, by expedients. Moreover, each expedient can be presented only in a limited form and on a case-by-case basis. (What makes good sense to one person may make no sense at all to somebody else.)

[W]e need a central theme or foundation to unify our many theories of the truth—some theme which has already served us well in the past. So we pick out the one which has been of the most value. In Buddhism, the Bodhisattva Vehicle, or Great Vehicle, has been of the most value. Accordingly, the Great Vehicle has two identities: one which is unified as an expedient, and one which unifies the three expedients as the true teaching. The former is the Great Vehicle, the Bodhisattva Vehicle, in relation to the other two vehicles. The latter is the one which is higher in value and embraces the other two by transcending any contrast between them. In this case, the Bodhisattva Vehicle may be a synonym for the One Buddha Vehicle.

Since the Bodhisattva Vehicle is the basis for the unification of the three vehicles, it follows that the “hearers” and “private Buddhas” are themselves really Bodhisattvas without knowing it. So the Buddha says:

“Śāriputra! Some disciples of mine, who think that they are Arhats or Pratyekabuddhas, will not be my disciples or Arhats or Pratyekabuddhas if they do not hear or know that the Buddhas, the Tathāgatas, teach only Bodhisattvas.”

Notwithstanding the Buddha’s efforts, people failed to realize that the expedients they had been taught were only part of the vast and profound truth attained by their master. Gradually they divided into different schools or sects clustered around a particular teaching which they believed to be the ultimate. During his fifty-year teaching Sakyamuni had employed a wide variety of expedients. His disciples, who scattered far and wide, noticed that they had received different teachings. They began to argue among each other about which teachings and practices were the more correct.

To solve these disputes, Sakyamuni introduced the Lotus Sutra – his ultimate teaching. Its first purpose was to break the attachments his disciples had formed to their own particular ideas. That is, Sakyamuni proclaimed that all he had previously taught were only expedients. They were partial truths, not the whole. They were separate “Vehicles.” Now they must be unified into One Vehicle, the Buddha Vehicle. This concept of the One Vehicle is the central thought of the Lotus Sutra and the chief idea presented in this chapter.

The Dharma which was attained and taught by Sakyamuni is the Universal Truth or Law, which must be acknowledged by every human being. There is only one Truth. However, so that people could understand it better, Sakyamuni expounded the one Truth in various ways, according to the capacities of his listeners. The varieties in Sakyamuni’s teaching show that the Truth is not rigid; rather it is flexible enough to be presented in different forms, according to the circumstances, despite its oneness. This is the reason Sakyamuni’s numerous sutras can be said to compose one and the same teaching. Unfortunately, sectarians, who did not understand the unity of Truth, began to turn these partial truths against each other and vie with each other for superiority. Their teachings, diverse as they may appear, are still united in the single teaching of the Buddha. The concept of the unification of doctrines is the very core of the teaching of the One Vehicle.