Chih-i ‘s sinification of Buddhism is reflected in the theme of the One Buddha-vehicle. This theme that is adhered by Chih-i throughout his work is about the relation of one with many. Although many are indispensable, the one is to be aimed at. This is to say that various doctrines in the teaching of the Buddha are necessary in terms of suiting various abilities of living beings, but one has to bear in mind that all these doctrines serve to lead beings to eventually attain the One Buddha-vehicle. The concept of oneness as the ultimate goal that unifies multitudes is prominent in Chinese thought. In the Book of Changes, a similar expression of this theme concerning oneness is also delivered:

“In the world there are many different roads but the destination is the same. There are a hundred deliberations but the result is one.”

The philosophy of Wang Pi is also concerned with the oneness, but this oneness is identified with nothingness, and is taken by Wang Pi as the force unifying myriad things in the universe. We are reminded that the Ultimate Truth as the One Buddha-vehicle in Chih-i’s theory functions as the unifying force under which the Three Vehicles (śrāvaka, pratyekabuddha, and bodhisattva) are united. (Page 159)