Hell
Those who have died and gone to Hell are not allowed to come back and warn people of its existence {Update: After Death Experiences}. Those who say they believe in God, but don't believe in a real place called Hell where sinners live eternally in heat and anguish don't really believe in God; for Jesus Christ taught us that Hell is very much a real place, (ST. Luke 16: 19-31), (ST. Luke 12:4-5).