Why the need to:
Believer believe that after a person passed on, his soul still exists. However, some souls are “trap” in-between the netherworld and human world as no one pay respect to these souls. Thus, they will become “unclaimed souls”.
A person may have unintentionally offended these souls, (example accidentally kicked on an urn, stepped on prayers offering, etc.) resulting the person to fall sick.
Hence, believer will need to engage a Taoist priest to conduct ritual to give offering to these souls to appease their anger and to send them to the netherworld.
During the Chinese 7th Month festival, some believers will engage Taoist priest to conduct ritual for these “unclaimed souls” to enable them to enter into reincarnation. This is also one of the rituals that the Chinese place great importance to.
Video- Ritual conduct during the Hungry Ghost Festival.