梵網經菩薩戒本疏 6.57

6.57

初、制意者，菩薩理宜心如金剛護持禁戒，令眾中油鉢一渧無遺，海內浮囊纖塵不毀，何容惡心婬盜殺謗？為護本戒制茲末禁，通結二罪故須制也。

First, the intention of instituting the precept: A bodhisattva should rightly have a mind like vajra to uphold the prohibitive precepts, making sure not a single drop is lost like the bowl of oil in the crowd, and not a speck of dust harms it like the floating buoy in the ocean; how could they with an evil mind commit sexual misconduct, theft, killing, and slander? To guard the root precepts, these secondary prohibitions were instituted, universally adjudicating two offenses; hence it had to be instituted.