Ryan explained this pretty good. I will copy/paste an excerpt from one of Bruce's articles which talks more about this.
The BST's are territories that lie in what he calls Focus 25. Here is more information from Bruce:
Focus 25Further from the shores of our physical world is Focus 25, also called the Belief System Territories. Here, people are drawn into an afterlife existence by a structure of beliefs they held while physically alive.
Each area of Focus 25 is like a far-off, isolated island inhabited only by those who shared the same set of beliefs. They have almost no contact with others living elsewhere in the New World of our afterlife. Their surroundings appear to them as real as physical Earth does to us, and supports whatever belief structure they mutually hold.
Devil's IslandNot so many years ago, penal colonies were established on remote islands as a way of isolating criminals from the rest of us. During another partnered exploration with Rebecca, we went looking for Max and landed on the island reserved just for folks like him. Max had been a psychiatrist with a dark side in his most recent lifetime. After death, he was drawn into one of the hells of Focus 25 - the one for emotional sadists.
During his physical lifetime, Max probed your deepest, darkest fears and it didn't matter if you were a patient or a friend: he was always hoping to find something he could later use to inflict emotional pain. For example, say you were a gay City Mayor, afraid your constituents might discover your secret; and say Max also knew a newspaper reporter who feared homosexuals were leading the country to damnation. Max would see to it that the two of you met in a situation where he could watch the excitement. He'd give both of you reason to fear the encounter before you met and then take great delight in watching the fireworks.
At death, Max's way of life drew him to his island hell in Focus 25. To him, this place was real with houses, trees, cars and streets forming a reality indistinguishable from Earth. There were other people there, too, but only those who shared Max's emotionally sadistic nature. During our failed attempt to retrieve Max, I witnessed scenes from his life there. In one, he sat at a secluded restaurant table and watched with glee as two men came to blows over something Max had choreographed. In the very next scene, someone else sat at the secluded table, taking delight in watching two men, Max being one of them, suffering through an emotionally painfully experience.
During this exploration I discovered how people are drawn into these Focus 25 hells, and how they can escape to a better place.
Hollow HeavensThere are other remote, isolated islands in Focus 25 called Hollow Heavens, and on one of my voyages I met a man who'd escaped one. He called them "hollow" because they weren't the real thing, and they described his existence there. He'd been a minister in a small, fundamentalist sect of Christianity during his most recent physical lifetime, and when he died he entered the Heaven he'd preached about. All his needs, food, clothing, shelter and more, were provided for without the need for him to work. There was only one catch: he had to continue to espouse and practise the beliefs he'd preached during his physical lifetime. If he didn't, he was told upon arrival that he could be cast into outer darkness - in other words, sent to Hell for eternal punishment. That was all fine with him, and since he'd been a minister during his physical lifetime he was given a congregation and a church where he could continue to preach and tend his flock.
All was well until a cohabiting couple in his congregation refused to be married. According to the beliefs he taught, a man and woman had to be married in order to live together. But pointing to an incongruity in his beliefs, the couple explained that in the Bible Jesus said no one was taken or given in marriage in the Kingdom of Heaven, and on that basis they refused marriage or separation.
One Sunday morning, in front of his entire congregation, the minister attempted to humiliate them into compliance by threatening to cast them into Hell if they refused a marriage ceremony. The couple stood in front of the congregation and said that, given the choice between going against the biblical word of Jesus or giving up their love for each other, they'd rather be sent to Hell. With no choices left to him, the minister performed the casting-out ritual and the couple disappeared into thin air.
Later, troubled by what he'd done and seeing the incongruity pointed out by the couple, the minister prayed for guidance. Jesus appeared to him, and what He said caused a growing rift in the belief structure that held the minister in his hollow heaven. Eventually the minister was also cast out, but he discovered to his surprise that Hell was not his final destination.
Escape from a hollow heaven island of Focus 25 requires recognition of inconsistencies within the belief structures held by the inhabitants. Leaving there usually results in entry into the Focus 27 realm.
This information was taken from this page.