金光明經文句記 2.339

2.339

五、「有四」下，佛坐表覺智。本有四德，即是三諦以為所坐；修得四德，即是三智以為能坐，故用佛表。

Fifth, from "there are four" down, the Buddha's sitting represents the wisdom of enlightenment. The four fundamentally existent virtues are the three truths serving as that upon which one sits; the four virtues attained through cultivation are the three wisdoms serving as that which sits; hence it is represented by the Buddha.