Isaiah envisioned the final days of the judgment period when the resurrected billions will receive their call to participate in God's plan. These resurrected multitudes will be counted among God's elect—made participants in His Master Plan, and given the opportunity to enter God's Family (verses 22-23). They will then have a close relationship with God the Father (verse 24).
Imagine the astonishment of those resurrected at the beginning of this period of judgment. Each person will be in his first moment of consciousness since death. At first, some may think they are in heaven, hell, or purgatory. Most will simply be confused—bewildered.
Nothing that many had been taught about an afterlife will turn out to be true. Faced with undeniable evidence that their old teachings and ways were false, they will be more willing to start over and be taught the truth. Untold millions who have not had any religious teaching whatsoever will start learning from scratch.
Who will teach these thousands of millions? Millions of teachers who will have been born into God's Family in the first resurrection and during the Millennium!
Those resurrected to mortal life will then undergo a process of conversion similar to that of Christians today. They will be taught God's laws and will learn they are guilty of sin and deserving of the death penalty.
They will learn of God's mercy, and that Christ paid the penalty for them, if they will accept His payment. The vast majority will repent.
Upon repentance and faith in Christ as their personal Savior, they will be forgiven, and God's Spirit will be given to them. Then they, as children of God, can begin growing spiritually—developing God's holy, righteous, and perfect character within them.
Unlearning all the falsehoods learned in their first life and learning God's true ways will take time. And building character will take time, because character can be developed only through time and experience.