無量壽經優婆提舍願生偈註 2.187

2.187

經始稱「如是」，彰信為能入；末言「奉行」，表服膺事已。論初「歸禮」，明宗旨有由；終云「義竟」，示所詮理畢。述作人殊，於茲成例。

A sūtra begins by stating 'Thus' to show that faith is that by which one can enter; at the end it says 'undertook to practice it' to express that having taken it to heart, the matter is complete. A treatise at the beginning 'takes refuge and pays homage' to clarify that the central doctrine has a source; at the conclusion it states 'the meaning is concluded' to indicate that the principle expounded is finished. Authors differ, and in this they establish the precedent.