Chinese Cultural Studies:
from Edward Conze, ed., Buddhist Texts through the Ages, (New York: Harper Torchbooks, 1964), pp 142-143, repr in Albert M. Craig, et al, The Heritage of World Civilizations, 2d ed., (New York: Macmillan, 1990), p. 310
[Craig Introduction] The Lotus Sutra (Saddharmapundarikasutra), "Lotus of the True Dharma" is one of the best-loved sacred texts of Mahayana Buddhism. Its original Sanskrit text was translated many times into Chinese (the earliest being in 225 CE), as well as into Tibetan and other languages. The following passage is key one for the development of the idea of the cosmic form of the Buddha. Note that "Tathagata" "(which means "Thus Gone", ie, having achieved Nirvana) is one of the titles of Buddha.
Fully enlightened for ever so long, the Tathagata has an endless span of life, he lasts for ever. Although the Tathagata has not entered Nirvana, he makes a show of entering Nirvana, for the sake of those who have to be educated. And even today my ancient course as a Bodhisattva is still incomplete, and my life span is not yet ended. From today onwards still twice as many hundreds of thousands of Nayutas of Kotis of aeons must elapse before my life span is complete. Although therefore I do not at present enter into Nirvana (or extinction), nevertheless I announce my Nirvana. For by this method I bring beings to maturity. Because it might be that, if I stayed here too long and could be seen too often, beings who have performed no meritorious actions, who are without merit, a poorly lot, eager for sensuous pleasures, blind, and wrapped in the net of false views, would, in the knowledge that the Tathagata stays (here all the time), get the notion that life is a mere sport, and would not conceive the notion that the (sight of the) Tathagata is hard to obtain. In the conviction that the Tathagata is always at hand they would not exert their vigor for the purpose of escaping from the triple world, and they would not conceive of the Tathagata as hard to obtain.
Hence the Tathagata, in his skill in means, .has uttered to those beings the saying that ''Rarely O monks, do Tathagatas appear in the world." Because during many hundreds of thousands of Nayutas of Kotis of aeons those beings may have the sight of a Tathagata, or they may not. And therefore, basing my statement on this fact, I say that "Rarely, O monks do Tathagatas appear in the world." To the extent that they understand the rarity of a Tathagata's appearance, to that extent they will wonder (at his appearance), and sorrow (at his disappearance), and when they do not see the Tathagata, they will long for the sight of him. The wholesome roots, which result from their turning their attention towards the Tathagata as towards an objective basis, will for a long time tend to their weal, benefit and happiness. Considering this the Tathagata, although he does not actually enter Nirvana, announces his entering into Nirvana, f or the sake of those to be educated. And that is a discourse on Dharma by the Tathagata himself.. When he utters it, there is in it no false speech on the part of the Tathagata.
[Lotus Sutra: 15, 268-272]