Taken from the "Urantia Papers", the Celestials tells us;
The material self, the ego-entity of human identity, is dependent during the physical life, on the continuing function of the material life vehicle, [the body]. .....
[Note: Material self, the evolving personality of the mind, deemed the ego of human identity, is dependent upon the existence of the body believed to be the self. The ego exists only as long as its material self, the body exists.]
But selfhood of survival value, selfhood that can transcend the experience of death, is only evolved by establishing a potential transfer of the seat of the identity of the evolving personality from the transient life vehicle, the material body, to the more enduring and immortal nature of the morontia soul, and on beyond to those levels whereon the soul becomes infused with, and eventually attains the status of, spirit reality.
[Note: Morontia is the training worlds for souls evolving. It is said to exists between the material and the spiritual worlds. This place is understood to have been mentioned in Jesus' "A Course in Miracles" as "the Gap".]
This actual transfer from material association to morontia identification is effected by the sincerity, persistence, and steadfastness of the God-seeking decisions of the human creature.
Note: This teaching correlates to the teachings that we are part of God because his spirit is part of our mind. See video teaching "The Spirit in Our Mind, Is Part of God"