Why do Souls Stay Behind?

Below are excerpts from Wanda Pratnicka's book
"Possessed by Ghosts - Exorcisms in 21st Century" 

Unfortunately, most souls that have left their physical bodies don't pass straight through death's curtain to the other side. Worse still, the number of souls left suspended between Heaven and Earth, souls which for a variety of reasons declined to go to God, is constantly increasing. There are many reasons for this and I shall talk about each of them in turn.
The most important factor is that after death, these souls either don't know or don't believe that they died. For them nothing has changed. They missed their own deaths and they think they're still alive. They are unaware of the fact that they could go to the Light. They assume that they are alive and therefore belong to the Earth.(...) 

One of the reasons I decided to write this book was that I wanted to communicate this knowledge and to help us understand things which are of such importance to us all. My task is to help readers prepare themselves and their loved ones for passing through death's curtain to the other side. We shall all, sooner or later, have to face up to the issue of our own deaths.
In Eastern cultures talking about death, about what awaits us afterward, is perfectly normal, an everyday thing. Even small children take part. This attitude means that death does not come as a surprise. This awareness protects the dying as well as those who remain in this life. It would be useful to have this custom introduced into Western culture. There would be far fewer solitary, wandering ghosts not knowing what to do with themselves, finding no help from anywhere in what is to them an incomprehensible situation.(...) 

Some souls are severely confused long before their deaths. When they come through death they're incapable of recognizing their true states. These tend to be the incurably sick who have been treated with powerful pain killers, as well as drug addicts and alcoholics. The mind of a sick person receiving painkillers is comparable to the mind of a drug addict. Even long after death they're incapable of being themselves. Even when they recover their senses they still lack knowledge about life after death.(...) 

The next reason why souls don't go to the Light is that they're afraid of being punished for what they did. Sometimes their sins are minor, but during their lives they believed in a cruel, vengeful and punitive God. Now they feel unworthy of receiving forgiveness. Even though waiting for them at the moment of death there is a magnificent escort consisting of their spiritual guides and dear ones who died before them as well as the loving Light, they turn away and refuse to go further. They do not believe that God could forgive them their sins. This comes from the fact that they were unable to forgive them themselves.(...) 

The next very large group of abiding ghosts are the souls who during life did not believe in God and therefore had no-one to go to after death. They thought that life finishes in the grave, after which all that awaits is the abyss, nothingness. Other souls believed very deeply in God but thought they would lie in their graves till the day of the "Last Judgment" and only then would they rise up from the dead and go to "Heaven". They have, therefore, become victims of what they believed in or specifically of what their religion told them to believe in. They now feel deceived, not knowing what to do with themselves. Should they wait for the Judgment? For punishment? But where? In the grave? They live on, so they can't wait in abeyance. They've ascertained all this only after death when it is a little too late. You'll ask: "Too late to do what?" To go to the Light. It was at the moment of physical death that they should have decided where they would go.(...) 

Probably the largest group of souls remaining in the world of ghosts after death are all those who during their lives were so attached to earthly matters that they're incapable of freeing themselves from them. These matters can be material or non-material. It can be a house, a car or other possessions. Everyone has surely heard of haunted houses and the ghosts that terrorize them. Others loved to eat, drink, take drugs, indulge in sex or gamble to excess. Others again were too fond of making decisions for their near and dear ones, butting into everything so now they find it too hard to surrender their authority.
Another reason for ghosts to remain is a desire to put right the errors they made during their lives so far. They think that by staying on this side they will have an opportunity to mend what they did badly. (...) 

Some souls find it hard to leave the Earth because they've left someone who, in their opinion, should be looked after; these might be a parent of a small child, or a solicitous child with elderly and lonely parents and so on.(...) 

The souls described above remain on the Earth because that is the decision they took. There is, however, a large number of souls who would dearly like to pass through to the other side, to "Heaven", but are prevented from doing so by the despair of their dear ones. These souls are torn between their own good and the good of those they left. They may even be aware that it would be better for everyone if they did leave, but the living won't let them. We must remember, therefore, even during mourning and despite our sorrow, to think of those who have a right to leave. We do so in order not to harm ourselves or them.(...)