The judgement mentioned in Matthew 25:31-46 is different from the great white throne judgement which will be the final one issued by the King of kings and Lord of Lords, Jesus Christ. This ultimate judgement (Rev 20:11-15) is primarily for the dead unbelieving sinners. The three realms sea, death and Hades will give up their dead to be judged by the Lord according to their works because of their rejection of Christ's atonement when they were alive. Along with the dead, death and Hades are judged and cast into the Lake of fire.
The judgement mentioned in Joel 3.12 and Mat 25:32 is for the people who are alive during the time of the Lord's open Second coming in the glory along with His angels soon after the battle of Armageddon (Rev 16:14, Rev 16:16; Rev 19:11-15, Rev 19:19-21, Joel 3:12). The Lord will carry out this judgement in two phases.
The first phase will be the judgement of the believers alive during the Second coming of the Lord as mentioned in Mat 25:19-30. The careful believers who are faithful slaves of the Lord will be given authority over many things along with the overcoming saints of all ages. This role of authority is akin to the role of angels in today's age of grace as ministering spirits in the spiritual realm (Hebrew 1:14). On the other hand, the careless believers will be transferred to the realm called outer darkness where there will be weeping and gnashing of teeth (Mat 25.30). The punished believers who will suffer the loss of the millennial kingdom will join the believers (who overcame and are part of the kingdom) in the new heaven and new earth as promised by the Lord to all who believed in His name (John 3:16).
The second phase of the judgement is mentioned in Mat 25:31-46. Here the Lord Jesus Christ will appear with His angels and gather all nations which will be remaining post the battle of Armageddon. It is understood these gentiles will have never believed in the Lord Jesus Christ and yet are not part of the armies of the Antichrist annihilated in the war. Among them the Lord will separate the goats and the sheep. The sheep represent the people who will be merciful and compassionate towards the brothers of the Lord (believers) and took care of them during the tribulations, while the goat represent the unkind and hateful ones who will hate the brothers of Jesus Christ. The goat population will perish in the lake of fire soon after the perishing of the Antichrist and the false prophet mentioned in Rev 19:20. They are followed by the dead sinners who will be judged by the Lord on the great white throne (20:10-15)
For God, who said, “Let light shine out of darkness,” made his light shine in our hearts to give us the light of the knowledge of God’s glory displayed in the face of Christ.
2 Corinthians 4:6 NIV
https://bible.com/bible/111/2co.4.6.NIV
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