According to the Ullambanapatra Sutra, when Maudgalyayana, a chief disciple of Sakyamuni Buddha, was unable to alleviate the suffering of his mother in the realm of hungry ghosts, the World-Honored One told him that the only way to deliver his mother from the pains of suffering is to rely upon the strength of monastics in all directions in their cultivation of meritorious virtues. The Buddha instructed his disciples to dedicate an elaborate offering of food to all Sangha members in the names of his parents from the past seven lifetimes as well as the present lifetime because the practice of Sangha offering has the power to transform and deliver all sentient beings.
This is the origin of the annual Sangha Day celebration that is held as part of the month of filial piety (between July and August in the Gregorian calendar). Making offerings to the Sangha is viewed as a very meaningful and meritorious act as it allows the Sangha to practice without obstructions and it cultivates merits for ourselves and our ancestors.
It is believed that the merits acquired from making offerings to the sangha could liberate the deceased from the three suffering realms and allow the living to enjoy a life of abundance, good fortune and longevity.