金剛般若波羅蜜經註解 1.191

1.191

此經非大乘根器不能持誦，而持誦所感功德豈常人可聞？聞必狐疑不信，故不具說，蓋此經之義趣與其果報不可思議故也。

Without the capacity of the Mahāyāna, one cannot uphold and recite this scripture; how could ordinary people bear to hear of the merit induced by upholding and recitng it? Hearing it, they would inevitably harbour suspicious doubt and not believe; hence it is not fully spoken, because the import of this scripture and its fruition are inconceivable.