首楞嚴義疏注經 8.285

8.285

三也。三世果人入祕密藏以此為因，密之因也。又此大定具一切行，而非凡小之所能知，故名為密，密即因也。三世如來以此法門為究竟說，故名了義。此即約人法以立名也。

Third. The realized persons of the three periods enter the secret treasury taking this as cause—hence 'the cause of the secret.' Furthermore, this great samādhi is endowed with all practices and yet cannot be known by ordinary people or Hinayānists; thus it is called 'secret.' 'Secret' is precisely 'cause.' The Tathāgatas of the three periods take this Dharma-door as their ultimate discourse; hence it is called 'the definitive meaning.' This, then, establishes the name in terms of persons and Dharma.