[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.”