Many ancient cultures have the tradition of ancestral worship. Some Sanatana Dharma Sampradayas (traditions) and beliefs are explained here. In some Sampradayas, Pitru Vazhipadu (ancestral worship) is more important than even Daiva vazhipadu (divine worship).
Once the body dies, what happens to the imperishable Atma (soul)? It can go to a better or worse place, or be reborn in the same place (earth) in a better birth (a good family) or a worse birth (a bad family or a non-human birth), or remain in deep sleep (MahaNidhra) awaiting a body, or in the worst case scenario, remain conscious without a body. The worst case scenario can occur, say during suicides, resulting in the worst suffering.
When some saints pass, they will have a trickle of blood on the top of the head, indicating the exit to the highest place. Some may pass peacefully with the eyes looking upwards towards the center of the forehead, or with an open gaping mouth. These are higher places. A peaceful passing is an indication of passing to a higher place.
Some may pass with the body in excreta. This is an indication of passing to a lower place.
After passing, the top of the body's skull is slightly manually cracked during the cremation process, in India, to allow the Atma to pass to the highest abode if possible. In a lack of religious freedom, this religious practice is banned in multiple Abrahamic countries that believe in bodies or ashes being raised up from the dead, & consider this 'body mutilation'. In contrast, Hindus cremate the body & mix the ashes in a holy river or the ocean, leaving no trace. If the Atma is conscious & lingering in a subtle body, anguished at the loss of the physical body, complete erasure goads it to move on.
Every person is born with multiple debts. One of these debts is to the Pitrus, who helped provide the current body.
As a ritual, one needs to do Dana (donate) every day. The Kolam (Rangoli) decoration with rice flour is a donation to the insects. The other is feeding the birds, specifically crows. Crows are a medium to fulfill the debt.
As another ritual, every Amavasya (new moon), the male with a passed father does Pitru Tarpanam for the ancestors, along with food restrictions or fasting on that day. Every year, on Bhishmaashtami, everyone performs Bhishma Tarpanam, since Bhishma didn't have any kids owing to his oath.
Every year, the eldest male performs a yearly ceremony. Other members have to join. If owing to a family rift, if a sibling breaks away & does it separately, each sibling has to do it separately every year onwards. In the ceremony, food is offered to the Pitrus called Pinda Daanam. The mediums of offering are Agni (fire) & Jala (water). Naga Sadhus offer Pinda Daanam to themselves while alive, implying that the death of their previous body & their rebirth.
If the Pitru ended up in a worse situation after passing, it will eagerly await this offering for some relief from suffering. Without the relief & prolonged suffering, it may curse the earthly descendants for not fulfilling the debt. This can result in suffering for the earthly descendants. This can come in the form of different forms of suffering, such as physical & mental health issues, accidents & injuries, missing folks, loss of career or wealth & in extreme cases, loss of loved ones in an untimely manner. If you notice a lot of issues in the extended family, this could be a result of Pitru Shapam. This is also a theme in Jyotisha.
The Daivas through Daiva worship will sometimes modify or soften the blow, but they will not fully eliminate it. This theme recurs in the Puranic stories. Hence, Pitru worship is considered top priority for a happier material life.
Further, the ceremonies need to be performed in the Karma Bhoomi of Bharatha for full effect. In other Bhoomis, the efficacy is reduced. Some folks travel to India yearly to perform rituals.
Whatever level the Pitru ended up in, the offerings will make their way to them. It could be an unexpected largesse as a gift or a bonus to a human, or a treat to an animal or bird or insect.
These ceremonies are unique to some Sanatana Dharma Sampradayas. Other old surviving cultures also have similar traditions.
