In order to understand and locate the different levels of the world of Spirit, as described in this inspired book, I made myself this drawing.

The World of Spirit

Some explanations (confirmed by other sources) complete this drawing:

At terrestrial level we receive inspirations from the lower astral and of the "over me" A "over me" is a group of simple souls developing affinities between them. Their number and their experience depend on the quality of the terrestrial "vehicle" to which they attach themselves. Intimately sharing his joys and sorrows, they give him more or less judicious advice.. It is the quality of our thoughts and deeds that determines the inspirations we primarily attract.
We notice it or not, but the thoughts we send out are always picked up, on one level or another.
At the death of the body, the soul passes on a particular plane, beyond any influence: the space of decantation. There she rests, then makes her self-judgment. Finally, knowing who she really is, quite naturally, she goes to a group whose members have the same aspirations.

 « (...) Within the Spirit, all the structures that bring people together also exist, and the levels of evolution are as varied as on your plane. Some spheres are "lower" than others, we prefer to say more loaded, heavier, closer to you in short than the spheres detached from physical contingencies. »  [ "To those who seek" ]

A wandering soul can be welcomed by a group, which it will leave on its own if it does not feel well there. l'être qui est sur terreUnder the instigation of the being who is on earth, entities from higher planes can participate in the elevation of the group. Some, out of love, can remain there.

 « (...) Also, when you question me, me, your mother, it is not Louise de la Terre who answers. It's a little her and a lot more. It is also as if you were questioning yourself. »  [ "To those who seek" ]

In the same way, alliances can be established between "over me", with for tangible demonstration on the terrestrial plane a physical, intellectual, spiritual bringing together between the concerned vehicles (beings living on earth).

The higher the level, the more global the vision.
The "Father" : « Beyond discord and dissension is the Spirit of men who have understood. We are disembodied beings, former women, former men, once made of flesh. Coming from the human species, we are still part of it.
 (...) Like the process of distillation, where the most subtle separates from the coarsest, we rise towards God, while preserving our affinities with our original environment. »  [ "To those who seek" ]

Exceptionally, a Father can manifest himself to an incarnated being. He will be perceived according to his beliefs, his education (he who has no religion will see a light).