The Last Great Day helps us understand God's plan for the salvation of the majority of mankind, all those who have lived and died in six thousand years without being called, without having a real chance for salvation. All these will come up in the white throne judgement, brought back to life, and will have the opportunity to learn the truth without Satan around to deceive them, and they can be saved and be given eternal life with Christ and the saints forever (Ezekiel 37:1-14, Revelation 20:5, 11-15).
The white throne judgement is a blessing for mankind, enabling everyone who has ever lived to have a chance to be saved. But it is also a blessing for the members of the Church of God.
Most of us have had loved ones that were never part of the Church, never called to salvation in this life. We have developed relationships, love, with family members and friends who have died, never being converted - mothers, fathers, sisters, brothers, unconverted mates, children, and even friends. We can rejoice in God's wisdom, power, and mercy that we can see them again, even those who have died, and they can be in God's kingdom forever with us, if they repent.
The relationships we develop in this life with those who have never been converted will not be in vain. We can see them again in the second resurrection. And if they believe God and repent, our relationships with them, our love towards them, can continue for eternity. This is a blessing, not only for them, but for us. We don't have to sorrow as the world sorrows over the loss of these loved ones in this life, if they have died.
And for those unconverted still alive, there is a chance for them to live into the millennium, and they can be converted at that time.
How great is God's love and wisdom!
Here are links to related chapters or sections in Preaching the Gospel:
The Last Great Day - the White Throne Judgment, Chapter 2