Prior to the introduction of Buddhism into China books written by the Three Emperors, Five Rulers, Three Kings, T’ai Kung-wang, Tan (The Duke of Chou), Lao-tzu and Confucius were called “sutras” or “classics,” through which people learned the proprieties: children’s indebtedness to their parents, and the relationship between rulers and the ruled. The teachings of these books were observed by the people, and heaven has accepted them. When one didn’t follow these dharma, he was punished as a disobedient child or an outlaw. When Buddhism was introduced from India, there arose a dispute between the two sides. One insisted that it should be accepted while the other argued that it should be rejected. The emperor summoned the two sides to debate the issue. The supporters of Buddhism refuted the anti-Buddhists. Since then whenever they debated, anti-Buddhists were defeated just as the sun melts ice, or water puts fire out. Eventually they no longer argued against Buddhism.
As Buddhism was thus introduced into China, it became clear that some scriptures were superior or more profound in content than others. That is to say, they could be divided into Hinayāna and Mahāyāna, exoteric and esoteric, or provisional and true sutras. For example, all rocks are inferior to any gold, and gold can be graded variously. No gold in the human world, however, equals the gold mined from the Jambu River. Even the gold from the Jambu River can never match the gold in the Brahma Heaven. Likewise, all scriptures of Buddhism are like gold: some are superior to or more profound than others.
Hinayāna sutras are like small boats, which can accommodate a few people but not hundreds or thousands. Moreover, they must stay close to this shore and can’t cross over to the other shore. They can only carry a small amount of cargo. Mahāyāna sutras are like larger vessels, which can carry easily ten to twenty people. Loaded with a large amount of cargo, they can sail from Kamakura to as far as Kyūshū or Mutsu Province (Aomori and Iwate Prefectures) in northern Honshu.
The true sūtra is beyond comparison to the other Mahāyāna sutras. It is like an enormous ship that, loaded with hundreds or thousands of people and a great amount of treasures, is able to sail as far as Korea. This is the one-vehicle teaching of the Lotus Sutra.
Oto Gozen Go-shōsoku, A Letter to Lady Oto, Nyonin Gosho, Letters Addressed to Female Followers, Page 112-114