法華玄論 2.28

2.28

Answer: The sons are of two kinds: first, those who have not lost their minds; second, those who have lost their minds. The sons who had not lost their minds heard the three guidings in their ultimacy and all attained understanding; the remaining sons who had lost their minds heard the three guidings and were not enlightened; therefore, through skillful means [the father] proclaimed his extinction and expounded nirvāṇa for them, whereupon they were finally able to accept the Path. If so, the Nirvāṇa-sūtra was spoken for people of the dullest faculties.