A person who does not perform sādhanā (Spiritual practice) of chanting the Name of God remains entrapped in one species of living beings for years together or becomes a slave to negative energies; whereas, a person who chants the Name of God at the time of death attains subsequent momentum.
When a person dies, the subtle energy present in the body is active in the form of subtle gases. These gases help the linga-dēha (subtle-body) to attain better momentum.
1. Individual who does not perform sādhanā of chanting the Name of God
Individuals that do not perform sādhanā of chanting the Name of God receive neither inner energy (subtle energy generated from chanting the Name) nor external energy (blessing oriented strength from the Guru or Deities). Such souls, with all their hopes and expectations intact, remain entrapped in the same species of living beings for years together.
Since these linga-dehas do not have protection of any kind, they are easily overpowered by negative energies and remain under their control for years together. For such linga-dehas to acquire further momentum, they need to be supplemented with external energy through shrāddha-karma (Ritual performed to appease linga-dehas of the departed ancestors).
2. Individual who chants God’s Name at the time of death
If an individual is chanting the Name of God at the time of its death, then due to a continuous flow of sāttvik energy in the body, instead of getting entrapped in Martyalok (Subtle region of existence of the dead), depending on its karma it gains further momentum.
Reference : Sanatan’s Holy Text, ‘Death and post-death rites’