Answer: It is a commonly accepted assertion among the scholars of our times that the Thus Come One invariably preached his teachings in p.553accordance with the capacities of his listeners. But in fact this is not how the Buddha truly taught. If it were true that the greatest doctrines were always preached for the persons with the most superior capacities and understanding, then why, when the Buddha first achieved enlightenment, did he not preach the Lotus Sutra? Why, during the first five hundred years of the Former Day of the Law, were the teachings of the Mahayana sutras not spread abroad? And if it were true that the finest doctrines are revealed to those who have a particular connection with the Buddha, then why did Shakyamuni Buddha preach the Meditation on the Buddha Sutra for his father, King Shuddhodana, and the Māyā Sutra for his mother, Lady Māyā [rather than the Lotus Sutra]? And if the reverse were true, namely, that secret doctrines should never be revealed to evil people having no connection with the Buddha or to slanderers of Buddhism, then why did the monk Realization of Virtue teach the Nirvana Sutra to all the countless monks who were guilty of breaking the precepts? Or why did Bodhisattva Never Disparaging address the four kinds of believers, who were slanderers of the Law, and propagate to them the teachings of the Lotus Sutra?
Thus we can see that it is a great mistake to assert that the teachings are invariably expounded according to the listeners’ capacities.
Question: Do you mean to say that Nāgārjuna, Vasubandhu, and the others did not teach the true meaning of the Lotus Sutra?
Answer: That is correct. They did not teach it.
https://www.nichirenlibrary.org/en/wnd-1/Content/66Such was the Buddha’s prediction. Accordingly, we find that there were seventy scholars in India who followed in the wake of Nāgārjuna, all of them major scholars. And all of these seventy scholars took Treatise on the Middle Way as the basis of their teachings. Treatise on the Middle Way is a work in four volumes and twenty-seven chapters, and the core of its teachings is expressed in a four-phrase verse73 that describes the nature of phenomena arising from dependent origination. This four-phrase verse sums up the four teachings and three truths contained in the Flower Garland, Wisdom, and other sutras. It does not express the three truths as revealed and unified in the Lotus Sutra.
Question: Is there anyone else who thinks the way you do in this matter?
p.554Answer: T’ien-t’ai says, “Do not presume to compare Treatise on the Middle Way [to the teachings of the Lotus Sutra].”74 And elsewhere he says, “Vasubandhu and Nāgārjuna clearly perceived the truth in their hearts, but they did not teach it. Instead, they employed the provisional Mahayana teachings, which were suited to the times.”75 Miao-lo remarks, “For demolishing false opinions and establishing the truth, nothing can compare to the Lotus Sutra.”76 And Ts’ung-i states, “Nāgārjuna and Vasubandhu cannot compare with T’ien-t’ai.”77
The Selection of the Time
Below is a reference for the unification of the three truths (or as I like to consider it mutual possession of three truths)
On the unification of the three truths
https://www.nichirenlibrary.org/en/dic/Content/U/17
and hopefully this is not seen as excessive but I thought it was a good synopsis. From a perspective of function I think the unification of the three truths is difficult to equate to previous teachings or deny the benefits and purpose it fulfills. All in accord with the sutra itself.unification of the three truths [円融の三諦] ( en’yū-no-santai): A principle set forth by T’ien-t’ai (538–597) based on the Lotus Sutra. It explains the three truths of non-substantiality, temporary existence, and the Middle Way as an integrated whole, each of the three containing all three within itself. T’ien-t’ai identified this as the view of the three truths revealed in the perfect teaching, or the Lotus Sutra, in contrast to the separation of the three truths, the view espoused in the specific teaching.
Separation of the three truths is the view of the three truths as separate and independent of one another. The truth of non-substantiality means that phenomena have no existence of their own; their true nature is non-substantial. The truth of temporary existence means that, although non-substantial in nature, all phenomena possess a temporary reality that is in constant flux. The truth of the Middle Way means that all phenomena are characterized by both non-substantiality and temporary existence, yet are in essence neither.
The unification of the three truths means that the truths of non-substantiality, temporary existence, and the Middle Way are inherent in all phenomena. T’ien-t’ai taught a form of meditation called the threefold contemplation in a single mind, aimed at grasping the unification of the three truths, eradicating the three categories of illusion, and acquiring the three kinds of wisdom (the wisdom of the two vehicles, the bodhisattva wisdom, and the Buddha wisdom), all at the same time.
All Mahayana schools adopt some version of the Two Truths theory, with one exception: the Tiantai school, which alone among all Buddhist schools moves from the Two Truths epistemology to a Three Truths model of truth. The Three Truths are actually three different ways of looking at any object or state. Each implies the other two, and each is one way to describe the whole of that object, including its other two aspects. This cup is a cup: that is provisional truth, conventional truth, local coherence. This cup is not a cup: that is ultimate truth, its emptiness, its global incoherence. To be a cup is not to be a cup: that is its Centrality, its Non‐duality, its Absoluteness. This cup is all things, all possible ways of being, all universes, as this cup.