We tend to overlook the reality that the spirit world and paradise are part, really, of the second estate. The work of the Lord, so far as the second estate is concerned, is completed before the Judgment and the Resurrection.
Since those who go to the celestial kingdom include, as revealed, those who "overcome by faith" (D&C 76:53), the same efforts and triumph would need to occur in the spirit world before they receive resurrection and the entitlement to enter the celestial kingdom. . . .
He gave us our spirit birth, bringing the first estate to all. He gave the gift to us of mortality, or the second estate, where all might be "added upon," leaving one-third of the host free to be rebels! (Abraham 3:26; Revelation 12:4). He provides in the spirit world a continuum of mortality's probation, the great opportunity for all. (The Promise of Discipleship, p. 111)