佛說盂蘭盆經疏 1.4

1.4

將解此經，先開四段：一教起所因、二藏乘所攝、三辨定宗旨、四正解經文。初中復四：一酬宿因故、二酬今請故、三彰孝道故、四示勝田故。

Intending to explain this sūtra, I first open four sections: first, the causes for which the teaching arose; second, the pitakas and vehicles by which it is subsumed; third, determining the central tenets; fourth, correctly explaining the sūtra text. In the first there are again four: first, to repay past causes; second, to respond to the present request; third, to demonstrate filial piety; fourth, to reveal the superior field.