The eighth day after the seven-day Feast of Tabernacles is the Last Great Day, a feast of God separate from, but connected with, the Feast of Tabernacles.
This day pictures the general resurrection of the dead, also known as the White Throne Judgment. It pictures a time, after the millennium, when the vast majority of mankind that had died are resurrected back to physical life. This is pictured by the valley of dry bones passage in Ezekiel 37:1-14.
This event is described in Revelation 20:11-15.
The billions who have lived and died since the time of Adam will be brought back to life. The billions who never had a chance to hear, understand, and believe the true gospel and repent and be converted, the billions that much of traditional religion has assumed are lost, will be given a chance for salvation. No one ever born will miss out on salvation because of circumstances of birth.
They will live in two worlds. They will have lived in this present evil world ruled by Satan - a world that practices Satan's way of life. And they will live in the general resurrection period (perhaps 100 years - see Isaiah 65:20) when Satan is put away and the whole earth is ruled by Christ and the saints in justice, peace, prosperity, and happiness. And they will be able to compare.
They will be able to compare their experiences with Satan's way and God's way, and they will be able to see, if they are willing, that God's way is better. And they can make their choice to accept the truth of God, to accept Christ and the gospel message, to repent, be baptized, and be converted, and be saved.
No doubt the majority will choose to be saved, but each person will have to choose.
But people will also have to choose to forgive. When the billions who have lived and died over centuries are brought back to life at one time, murderers and their victims will be alive together. Hitler will be alive with the millions of Jews who died in Nazi concentration camps as a result of his murderous policies. Hitler will have to repent if he wants to be saved, but if he does, his victims will have to forgive him if they want to be saved. That will not necessarily be easy.
But that is the choice people will have to make.
This is all part of God's great plan for the salvation of mankind.
This shows the wisdom, love, and power of God that He will use this plan to teach mankind a lesson that will enable the greatest number to be saved. It also shows God's fairness and justice that no one will miss out on an opportunity to be saved.
How great God is!