Chu-i Yung-san (Abiding in the one and employing the three) is the function related to the Subtlety of Benefits. This is spoken of by Chih-i in terms of the Buddha’s original vow. The Buddha vowed to expound the Three Vehicles in mundane world. This original vow of the Buddha denotes “abiding in the one,” and expounding the Three Vehicles denotes “employing the three.” (Vol. 2, Page 446)