The Hadean world is where we go when we die; in the Old Testament it is called Sheol, and in the New Testament it is called Hades or Hell. It isn’t the final resting place of man, but is the place where we go to await the day of judgment.
“And as it is appointed for men to die once, but after this the judgment…,” Hebrews 9:27. When a man dies, his fate is sealed as far as eternity is concerned; if he is approved of God, he will live eternally with him, and if not, his fate is the lake of fire. But in the meantime, as the judgment has not yet come, man goes to the Hadean world. This world consists of Gehenna, the bad place, and Paradise, the good place. These are not the final, eternal destination of man, but only the holding place until the judgment (it may be compared to our modern trials (in America): After the verdict is found in a trial, seldom is the sentence passed at the same time; usually, it comes some time later. Nevertheless, the man’s fate is already determined, as far as guilt and innocence is concerned).
We have been given a look into this world; Jesus reveals it in the parable of the rich man and Lazarus,
“There was a certain rich man who was clothed in purple and fine linen and fared sumptuously every day. But there was a certain beggar named Lazarus, full of sores, who was laid at his gate, desiring to be fed with the crumbs which fell from the rich man's table. Moreover the dogs came and licked his sores. So it was that the beggar died, and was carried by the angels to Abraham’s bosom. The rich man also died and was buried. And being in torments in Hades, he lifted up his eyes and saw Abraham afar off, and Lazarus in his bosom,” Luke 16:19-23.
Lazarus was carried by the angels to Paradise (here referred to as Abraham’s bosom); it is not a place that a man can get to, if he is not approved of God. The rich man is in torment.
“Then he (the rich man) cried and said, ‘Father Abraham, have mercy on me, and send Lazarus that he may dip the tip of his finger in water and cool my tongue; for I am tormented in this flame.’ But Abraham said, ‘Son, remember that in your lifetime you received your good things, and likewise Lazarus evil things; but now he is comforted and you are tormented. And besides all this, between us and you there is a great gulf fixed, so that those who want to pass from here to you cannot, nor can those from there pass to us,’” Luke 16:24-26.
The place to which a man goes in the Hadean world, there he must remain. He is fully conscious, and aware of his fate. Where the rich man is, he can’t escape; for he earnestly desires even a drop of water on his tongue, yet his fate is set. He can see Paradise, he can see what he missed. Lazarus, even if he desired to help him, is unable; a great gulf has been fixed by God between the two places so that none can pass, in either direction.
“Then he said, ‘I beg you therefore, father, that you would send him to my father’s house, for I have five brothers, that he may testify to them, lest they also come to this place of torment.’ Abraham said to him, ‘They have Moses and the prophets; let them hear them.’ And he said, ‘No, father Abraham; but if one goes to them from the dead, they will repent.’ But he said to him, ‘If they do not hear Moses and the prophets, neither will they be persuaded though one rise from the dead,’” Luke 16:27-31.
We have already received our full warning of what is to come. God has told us in His word, that is, in the Bible, and it is sufficient for our awareness of the Hadean world, and of eternity. And to show that someone coming from the dead wouldn’t convince them, Jesus has risen from the dead, and how many reject him?
This is not a story Jesus made up to teach a lesson; these are real places. This is shown in His words on the cross; for He says to the thief on the cross who believed, “Assuredly, I say to you, today you will be with Me in Paradise,” Luke 23:43.