Chinese Buddhists inherited a problem that Indian Buddhists never had in the same form. The scriptures arrived out of order, over four centuries, in translations of uneven quality, and they contradicted each other. The Buddha of one sutra says the goal is individual liberation; the Buddha of another says that goal is provisional. Since all of them were held to be his words, the contradictions had to be arranged rather than resolved.
Zhiyi's answer, the classification of the teachings, is the most influential solution anyone produced. He read the discrepancies as pedagogy: the Buddha taught differently at different stages of his career and to hearers of different capacity, so the canon records a curriculum rather than a set of competing positions. The scheme is conventionally summarised as five periods and eight teachings, sorting the scriptures both by when they were delivered and by the method and content of the delivery. The Lotus Sutra sits at the summit as the teaching in which the earlier provisional forms are acknowledged as provisional and gathered up.
The historical chronology is wrong, as everyone now knows: the sutras were not composed in that order and the periods are a construction. What the scheme did was let a reader hold the whole canon at once without discarding any of it, and give a principled reason for ranking. Every later East Asian school that claims a supreme scripture is arguing on ground Zhiyi laid out.