梵網經菩薩戒本疏 6.185

6.185

初、制意者，以戒是成佛，膳因彼教，理宜尊重。況是諸佛之母，如來所師，崇重之極，豈先於此？故須制也。

First, the intention of the precept: because the precepts are what achieves Buddhahood and nourishment comes from that teaching, it is reasonable that they be revered. How much more so since they are the mother of all Buddhas and that which the Tathāgatas take as teacher—what could take precedence over this utmost veneration? Therefore it had to be instituted.