法華論疏 2.92

2.92

別出甚深體，正以無上菩提為甚深體。菩提言忘慮絕，故稱甚深也。「又甚深者」下，前明當體甚深，今明二乘不測，故名甚深。

This specifically brings forth the essence of profundity, taking unsurpassed bodhi as the actual essence of profundity. Bodhi transcends speech and thought, and therefore is called profound. From 'Furthermore, "profound"' downward: the former clarified the profundity of its own essence; the present clarifies that the two vehicles cannot fathom it, and therefore it is called profound.