According to this explanation by T’ien-t’ai, since the essential section of the Lotus Sūtra is the essence of Buddhism, all other sūtras, be they Mahāyāna or Hinayāna, provisional or true, and exoteric and esoteric, such as the Nirvana Sūtra and Great Sun Buddha Sūtra, are Lesser Vehicle teachings. … Only the doctrines of the Tendai Sect comprise the Great Vehicle. It is because all sūtras except the Lotus Sūtra do not reveal the great dharmas of attaining enlightenment by persons of the Two Vehicles (śrāvaka and pratyekabuddha) and the concept of the Eternal Buddha.

Shōjō Daijō Fumbetsu-shō, The Differences between Hinayāna and Mahāyāna Teachings, Writings of Nichiren Shōnin, Doctrine 2, Page 192