大般涅槃經義記 9.158

9.158

下對設難。難意如何？佛具根力說應當機，何因緣故作不定說，令未來人各執聖言起諍斷善？於中先舉二十一對諍論之言，下責如來何故今日作不定說。

Below, he poses the challenge in response. What is the intention of the challenge? The Buddha is endowed with the power of faculties and his preaching responds appropriately to capacities; for what cause and condition did he deliver indeterminate teachings, causing people of the future each to grasp at the sacred words and give rise to disputes, severing their roots of goodness? Within this, he first adduces the statements of the twenty-one pairs of disputations, and below he reproaches the Tathāgata for why he gives indeterminate teachings today.