“Good men, in the past I sat upright for six years under the bodhi tree in the place of enlightenment and was able to gain supreme perfect enlightenment. With the Buddha eye I observed all phenomena and knew that this enlightenment could not be explained or described. Why? Because I knew that living beings are not alike in their natures and desires. And because their natures and desires are not alike, I preached the Law in various different ways. Preaching the Law in various different ways, I made use of the power of expedient means. But in these more than forty years, I have not yet revealed the truth. ... Good men, ... I rose up from under the kingly [Bodhi] tree, proceeded to Deer Park in Varanasi, and turned the wheel of the Law, preaching the four noble truths for Ajnata Kaundinya and the other five ascetics ... During the middle period, both here and in various other places, for the sake of the monks and the host of bodhisattvas I expounded and set forth the twelve-linked chain of causation and the six paramitas... And now once more I am here expounded this great vehicle Immeasurable Meanings Sutra.” (LSOC, p15-16)
This is another one of those signposts that T’ien-T’ai used to classify all of the Buddha’s sutras and this one clearly states that:
(i) Shakyamuni awoke to this Law when he sat under the bodhi tree.
(ii) Because of its difficulty and the difference in people’s abilities, he had to preach this sutra in various different ways prior to this moment.
(iii) In more than 40 years, he hasn’t revealed this truth – the truth he was awakened to under the bodhi tree.