I have confirmed that the Pusajie-yishu (菩薩戒義疏) by Zhiyi (智顗, 538- 597) is indeed the oldest of the Commentaries on Fanwang-jing (Brahmāʼs Net Sutra, 梵網經). Zhiyi uses a unique structure of the Essence of Precepts (戒體), called ‘The Non-apparent Form of a sacred Non-indicative Form’, in the Yishu, which is different from the one shown in his previous books. The Essence of Precepts, in the Yishu, has a unique structure in which its presence or absence is determined according to Two Teachings, namely Expedient and True (權實二敎). The Yishu does not recognize the existence of the Essence of Precepts as the True Teaching, but instead considers it to be the Expedient Teaching. In other words, although the Mental Dharma (心法) represents the Essence of Precepts as the True Teaching, the Essence of Precepts is actually a structure that uses the Form Dharma (色法) as the Expedient Teaching for distributing the Fanwang-jing. And this is a temporary Form Dharma that is different from the Form Dharma of the Lesser Vehicle (小乘). This means that to find the Buddha-nature (佛性) of the Mental Dharma, and attain the Essence of Precepts of the Marvelous Contemplation of the Middle Way, can only be accomplished through ascetic practices.

Zhiyi, Pusajie-yishu, Fanwang-jing, Essence of the precepts, Three causes of buddha-nature, Mental Dharma, Form Dharma