梵網經菩薩戒本疏 6.167

6.167

初、制意者，戒律制於內眾，為祕密之教法，外道惡人理非所聞，故須制也。別顯有三：一、輕自戒品；二、增彼惡見；三、令他毀謗。是故制也。

First, concerning the intention of instituting the precept: the vinaya precepts are instituted for the internal assembly as a secret teaching; tīrthikas and evil people in principle should not hear them, hence it had to be instituted. Specifically, there are three reasons: (1) slighting one's own category of precepts; (2) increasing their evil views; and (3) causing others to slander [the Dharma]. For these reasons it is instituted.