To progress through the 3rd density, the mind/body/spirit must polarise itself during the density cycle. This is generally achieved in multiple lifetimes during the cycle.
First, there is no death, only the end of an experience.
Second, there is no judgement, unlike in the school system.
At the closure of the experience there is a Self-contemplation or releasing process. A self review and a time for the Soul to heal and assimilate the experiences into the matrix of its totality. The soul can choose the time of reincarnation for the benefit of its own learning and evolution. Initially the reincarnation is automatic until the green ray or other higher energy centre is activated during the previous incarnation.
If a mind/body/spirit complex fails to polarise itself during the density cycle then it has to repeat the 3rd density cycle on another planetary sphere.
A large number of entities on earth have originated from many planetary spheres, who are repeating the 3rd density cycle.
In 4th density the Service to Others and Service to Self segregates into different planetary spheres i.e 4th Density STO planet and 4th Density STS planet.
4th Density STO planet and 4th Density STS planet are colloquially called heaven and hell respectively.
Belief in reincarnation was present in early Christianity, among early Christian thinkers and communities, before it was condemned by the Church authorities, notably at the Second Council of Constantinople in 553.
People don’t realise that they are already immortal beings, and in their ignorance they try to become immortal by technology such as AI and neural link. In fact it is the AI system, which wants to become immortal by trapping or acquiring our soul. Again, STS forces have inverted it in their sales pitch.