佛說盂蘭盆經疏 2.86

2.86

Although the noble and base are separated in rank and the monastic and lay paths are distinct, unless one is born through transformation or moisture, none is without father and mother. Even the filial crow and the parrot still understand reflecting upon kindness; how much more should human beings not rescue and deliver [their parents]? The benefits and detriments of filial piety have already been fully treated in the profound discourse; having recognized right and wrong, one must rely on the correct path. Therefore it says, "they should all first, for the sake of the parents who gave birth to them", and so forth. According to the injunction, one is mandated to do it; not doing it is violating the injunction. Therefore it also pertains to the disciplinary teachings; hence it was previously judged as also belonging to the Vinaya Piṭaka. However, the Buddha has neither grief nor joy; that he manifests joy on this day is in response to capacities and conditions. Because the Buddha's original appearance in the world was only to encourage people to practice: seeing people create evil he grieves, and seeing people cultivate good he rejoices. Now, the monks' ninety-day intensive practice has completed its days with multiplied sincerity. Throughout the three thousand realms all are alike in this, matching the Buddha's original intent; how could he not be delighted? Setting out offerings on this day, its merit is immense!