Ullambana is Sanskrit. It means "rescuing those who are hanging upside down." It's very painful to be hanging upside down, and so now we are going to rescue those who are that way. Rescue whom? We are going to rescue our parents and other ancestors from previous lives. We don't know whether our past relatives created merit, in which case they may have been reborn in the Land of Ultimate Bliss, or in the heavens, or among people as presidents or emperors; or whether they created offenses in which case they may have fallen into the hells, into the realm of hungry ghosts, or into the animal realm.
The fifteenth day of the seventh lunar month is the anniversary of the day when the Venerable Mahamaudgalyayana saved his mother from the hells. When his mother was alive, she didn't believe in the Triple Jewel. She killed many fish, turtles, shrimp and crabs and she was stingy and unwilling to give to those in need. Because of these offenses she fell into a hell of hungry ghosts. The Venerable Mahamaudgalyayana quickly sent her a bowl of food. She shielded the bowl with her left hand and used her right hand to take the food. However, once in her mouth, the food turned into burning coals which were impossible to eat. The Venerable One went to seek the Buddhas's help, and the Buddha told him to make offerings to the Sangha of the ten directions during the Pravarana (the last day of the summer retreat when Sangha members repent of their offenses before the assembly). Because of the Sangha's great virtue and awesome spiritual power, if one makes offerings to the Sangha, his parents and close kin in this life and seven lives past, will escape the three evil paths.
If you feel you have a big temper and too much "fire of ignorance," it is because your parents and other relatives from the past have not left suffering and attained bliss. Every day they help you get angry, and encourage you to commit offenses so that you can hurry up and join them. If you feel that this may be the case, you should take advantage of this opportunity to do merit and virtue to cross them over; and will cause all those in difficulty to leave worry and suffering and to eradicate obstacles from offenses. Moreover, on this day the merit and virtue derived from making offerings to the Triple Jewel is several million times greater than that on ordinary days.
In the West, there has rarely been a Way-place which held this kind of celebration. Every one of us should act as a filial descendant for our parents and ancestors of former lives.