When you die your astral body (or your Spirit) separates from your physical form. Also the connection between your vital energy stored on the astral realms is lost. This energy is what animates your physical body. But some of this vital energy is also stored here on the physical plane in the form of your aura. At the time of your death, as a reaction to the loss of a heartbeat, this energy stored in your aura is released.
This energy from your aura is able to pierce the separation between the physical and the astral worlds. The energy is able to combine with your vital energy stored on the Etheric Plane of the Fourth Density. Together they create a portal to the Astral Plane of the Fifth Density. Within this portal is a light bridge your spirit can utilize to cross to the Astral Plane, your principal home for your life between lives.
This light bridge is only active for an average of about 24 hours, depending upon how much energy the spirt brought with it to the physical plane. A less developed spirit would bring more energy and the bridge may stay active for a day or two longer. A more advanced spirit would need less time to cross over.
("How It Works" continued below...)
But even as spirits we have free will. We can choose not to cross if we so wish. Historically, about 10% of spirts exercise their free will and choose not to cross, although of late that percentage has increased dramatically. Over the millennia this has added up to a staggering number of spirits. Spirits that choose not to cross while their light bridge is active effectively become trapped. They are what we call ghosts. Our world had to be designed in this manner to preserve our free will.
Ghosts live with us on the Physical Plane of the Third Density of existence. This is where I differ from most teachers of esoteric knowledge, who think that upon death a spirit automatically ascends to an astral level, or a parallel existence to that of our own. That is simply not how our world works. Ghosts are right here with us and are subject to the same environmental conditions as are we.
All of these ghosts hold on to the negative energy they acquired during their mortal lives. This upsets the natural balance between good and bad energies on our planet. Moreover, it actually causes the spirit damage to remain here on the Physical Plane. Our bodies resonate at a frequency vibration that is in harmony with that of the Earth, but the Astral Body was not designed to remain on the Third Density without the physical protection of the mortal body. The longer they stay, the worse the damage.
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The ability to help an earthbound spirit cross over to the other side is something we all share. There are no special abilities needed and no special incantations or prayers required. Although none of that hurts if it helps to focus your intent. Because a clear and heartfelt intent is the only thing required. Usually all you have to do is to talk sincerely, earnestly and with love to the spirit you are aware is trapped to help them cross. What happens is when you demonstrate a clear intent to help a spirit cross to the other side, the rhythms of your heart actually change to create the frequency needed to expand your aura and generate the portal and the light bridge to the Astral Realm. Spirits in your presence can utilize the light bridge to depart the Physical Plane. Yes, this uses some of your vital energy but not enough to compromise your health, and it will quickly regenerate. Doing this with the company of others helps spread the vital energy drain.
The auras of most people can expand enough to help one or two spirits cross, or a handful within a group. Some experienced mediums can accommodate a few more. My aura expands enough and I am strong enough to handle millions of spirits at once. This gift is genetic and runs in my family. Currently there are a total of 39 genetic lines, passing the gift from a female carrier along the most direct bloodline. Only one individual in each bloodline is active at a time, and not all of the 39 active carriers are aware of their abilities. I inherited the gene from my mother. The gift was lost for more than three hundred years because of disuse but was restored within the past few years as light workers began to awake to their true callings. This ability was once honored among ancient peoples who understood the natural world more intimately. It is a natural and necessary gift that allows wayward spirits to continue on their eternal path.
This video explains the process of crossing over after death in a bit more detail.