妙法蓮華經玄義 8.115

8.115

Second, the gate of emptiness: this is analyzing direct causes and conditions in that teaching—ignorance, aging-and-death, the two truths of suffering and arising, the three designations being insubstantial and empty; breaking through provisional and real, all enter into the equality of emptiness, giving rise to the true untainted [wisdom]. Seeing the real through emptiness, emptiness is the gate of supreme meaning. Thus Subhūti, in his stone chamber, contemplated arising-and-perishing and impermanence, entering emptiness. Attaining the path through emptiness, he saw the Buddha's dharma-kāya; this is presumably what is expounded in the Tattvasiddhi-śāstra.