Question: "What does it mean that hell is eternal separation from God?"
Answer: The Bible is clear that there are two possible destinations for every human soul following physical death: heaven or hell (Matthew 25:34, 41, 46; Luke 16:22–23). Only the righteous inherit eternal life, and the only way to be declared righteous before God is through faith in the death and resurrection of Jesus Christ (John 3:16–18; Romans 10:9). The souls of the righteous go directly into the presence of God (Luke 23:43; 2 Corinthians 5:8; Philippians 1:23).
For those who do not receive Jesus Christ as Savior, death means everlasting punishment (2 Thessalonians 1:8–9). This punishment is described in a variety of ways: a lake of fire (Luke 16:24; Revelation 20:14–15), outer darkness (Matthew 8:12), and a prison (1 Peter 3:19), for example. This place of punishment is eternal (Jude 1:13; Matthew 25:46). There is no biblical support for the notion that after death people get another chance to repent. Hebrews 9:27 makes it clear that everyone dies physically and, after that, comes the judgment. Christians have already been judged and sentenced. Jesus took that sentence upon Himself. Our sin becomes His and His righteousness becomes ours when we believe in Him. Because He took our just punishment, we need not fear ever being separated from Him again (Romans 8:29–30). The judgment for unbelievers is still to come.
Second Thessalonians 1:8–9 says, “He will punish those who do not know God and do not obey the gospel of our Lord Jesus. They will be punished with everlasting destruction and shut out from the presence of the Lord and from the glory of his might.” The misery of hell will consist of not only physical torture, but the agony of being cut off from every avenue of happiness. God is the source of all good things (James 1:17). To be cut off from God is to forfeit all exposure to anything good. Hell will be a state of perpetual sin; yet those suffering there will possess full understanding of sin’s horrors. Remorse, guilt, and shame will be unending, yet accompanied by the conviction that the punishment is just.
There will no longer be any deception about the “goodness of man.” To be separated from God is to be forever shut off from light (1 John 1:5), love (1 John 4:8), joy (Matthew 25:23), and peace (Ephesians 2:14) because God is the source of all those good things. Any good we observe in humanity is merely a reflection of the character of God, in whose image we were created (Genesis 1:27).
While the spirits of those regenerated by God’s Holy Spirit will abide forever with God in a perfected state (1 John 3:2), the opposite is true of those in hell. None of the goodness of God will exist in them. Whatever good they may have thought they represented on earth will be shown for the selfish, lustful, idolatrous thing it was (Isaiah 64:6). Man’s ideas of goodness will be measured against the perfection of God’s holiness and be found severely lacking. Those in hell have forever lost the chance to see God’s face, hear His voice, experience His forgiveness, or enjoy His fellowship. To be forever separated from God is the ultimate punishment.