Claim. Spirits who died before reaching perfection cannot grow further on their own — because spirits can grow only through give-and-take with a physical self (see dp-spirit-grows-only-in-the-flesh-on-earth). Their resurrection requires returning to earth and cooperating with earthly people of similar mission; the spirit assists the earthly person to fulfill the mission, and both receive elevation. This is the mechanism of returning resurrection.
Elaboration. Per 2.3.1. The Purpose and the Way of Returning Resurrection: “According to the Principle of Creation, the growth of the human spirit requires two kinds of nourishment: life elements received from God and vitality elements received through give and take action with the physical self. Spirits can neither grow nor be resurrected apart from a physical self. Consequently, the spirits of people who died before they could reach perfection during their earthly life can be resurrected only by returning to earth and completing their unaccomplished responsibility through cooperation with earthly people.”
The cooperative payoff: “By assisting people of faith living on the earth to fulfill their missions, the spirits may complete their missions at the same time.” The Last-Days prophecy that the Lord will come “with his holy myriads” (Jude 14) is read as the mass descent of all unresolved spirits to participate in completion-stage resurrection alongside earthly people.
How it works experientially: “When people become receptive to spirits through prayer or other spiritual activities, the spirits descend to them to form a common base with their spirit selves and work with them.” Spirits then perform various works — spiritual fire, healing, trance, prophecy, deep inspiration — all “on behalf of the Holy Spirit, guiding people on the earth to accomplish the Will of God.”
This is the doctrinal anchor for the rest of §2.3 (growth-stage, completion-stage) and §2.4 (reincarnation reframing).
See also. dp-jtb-was-elijah-by-mission-not-soul-transmigration, dp-dead-rising-from-tombs-means-old-testament-spirits-appearing-to-believers