Reincarnation is an element of existence that was incorporated into the Constructs. The Creators felt it was important to allow individual Souls the ability to experience the uniqueness of Creation more than a single time. So there was a lengthy effort involved in determining how to allow or enable that to happen.
In the early times, the Soul was a singular Entity – there was no perceived need to treat a Soul as more than that. But as time progressed, and experiences continued, there appeared to be some level of advantage to being able to not just experience existence, but to still provide some level of coordination/communication/reporting to others that may reside in either the spirit or Energy realm. It was at that time that a Soul (particularly one that would incarnate) was allowed to “divide” into two distinct parts, an upper soul (a.k.a., higher self, or Oversoul). The Oversoul would remain in spirit form, while a “lower Soul” would have primary responsibility for the incarnate being.
So now assume that you have an interest in communicating with another Soul, somebody that you knew but that had passed from the Physical realm many years ago. Would you still be able to communicate with that individual, even if they had reincarnated into another person? The quick answer is yes. But there is a longer answer.
When a lower Soul (that part of a Soul that is responsible for the incarnate being) passes, the memories and personality of that lower Soul (which in reality formed the basis for the incarnate being) are then incorporated into the Oversoul, but not until the recently passed Soul goes through both the first transition period, and then the adaptation period (this is prior to the time of introspection). Up until the time of introspection, any Soul may engage in communications with another Soul, whether they are incarnate or not, and that communication generally occurs between the lower Souls. But when a Soul enters the period of introspection, the lower Soul basically transfers elements of its prior existence (or incarnation) to the Oversoul, and all of that information is then purged from the lower Soul, to begin preparing it for its further journeys (which could include something other than an incarnation).
If one desired to have a communication with a Soul that had entered the introspection state (or had already passed through this state), your Soul would no longer communicated directly with the lower Soul of the individual that you knew, you would be communicating with the Oversoul of that individual, because that is where the “essence” of that individual now resides. It no longer resides in the lower Soul, as that is, at that time, reserved for the experiences of the new incarnation. This may sound complicated, but it truly is not.
So why was this designed in this manner?
The Oversoul is the place where the memories of an individual resides, although copies are maintained in the akashic records. It is from the Oversoul that we experience things like deja vu, past life readings, and interactions with the higher Energy realms of existence. It is the Oversoul that controls the various portions of the Soul that reside below it, because it was the primary element of Creation. So when you seek to have communications with that portion of the Soul that you knew, it is the function of the Oversoul to either communicate directly with you (if the lower Soul has since reincarnated), or to oversee the communications in order to ensure that you are not provided information that is not included in any of the aspects of your own Soul Contract. For instance, it is the Oversoul that would prevent the lower Soul from providing you with next weeks lottery numbers, unless that information was expressly allowed to be told to you as a portion of your Soul Contract.
And it is the Oversoul that is ultimately responsible for the execution of your Soul Contract. It is also the Oversoul that will communicate with the higher realms of existence, and if need be, answer for the actions of the lower Soul. It is the Oversoul that is “accountable” and not the lower Soul, although the lower Soul is accountable to the Oversoul – even though they are, for all practical purposes, treated as a single entity.