首楞嚴義疏注經 6.450

6.450

真聖利物終不可測，以承佛制，不妄漏泄。此聖真因，唯聖自證，故云密因，未學之前不可輕說。陰有遺付者，不顯稱也。此開臨終密有表示，遣囑弟子，如求那屈指事。

How true sages benefit beings can never be fathomed. Because they uphold the Buddha's prohibition, they do not falsely leak it. This true cause of the sages is realized only by the sages themselves; hence it is called the 'secret cause' and must not be spoken of lightly before those yet to learn. 'Secretly leaving behind their final instructions' means not openly proclaiming it. This allows for secretly giving indications at the verge of death and bequeathing instructions to disciples, like Guṇabhadra bending his fingers.