梵網經菩薩戒本疏 4.48

4.48

初、制意者，菩薩理應謙卑敬養一切眾生，況於師長輒有輕慢，違行之甚故須制也。

First, on the intent behind the prescription: A bodhisattva in principle should humbly revere and attend upon all sentient beings; how much more so regarding teachers and elders should one not lightly show contempt and disrespect. Because this severely violates practice, it had to be prescribed.