Ah, dear ones.
I hope you don't grow tired of me expanding the dharma on the enneagram. But there's just a wee bit more that needs to be communicated on this matter; and it's my responsibility to publish this so that others can absorb and work on it.
As anyone who diligently studies Gurdjieff's esoteric system knows, the system is whole; that is, it is seamless, and every part is a reflection of all the other parts. We thus learn, perhaps to no one's surprise, that the three higher being bodies themselves comprise a triad which represents the precursor, on its own level, to a passage into Being.
What is surprising is that this clearly puts the Divine, in so far as it contacts us, in a specific place on the diagram of an octave; and that place is sol. What this explains to us is that even God is not complete; God himself is attempting to go further, purify himself, and acquire more wisdom, so that he can transcend his own transcendence. This apparent paradox is actually lawful and necessary; since all things are possible to God, this is also possible, and God is both subject to all laws and beyond them, in another apparent paradox.
Another important point in this diagram is that each aspect of man's being is a fractal, or fractional, but whole, representation of all the levels below and above it, and creates a connection between all of those fractions that correspond to it in terms of the rate of vibration above it and below it. Swedenborg called this the law of correspondences. What it means is that the material body, the physical body of man, is actually the mirrored image of the astral body on this level. In turn, emotion is the mirrored image of the mental body, and intellect is the mirrored image of the causal body. The three principles permeate the universe from top to bottom, because the law of three is one of the most fundamental and primary laws in operation.
Swedenborg understood this in a slightly different way that is in its own right entirely correct, and actually shed some light on the highest levels. Heaven, you see, is constructed of three levels in ascending order: a physical level, an emotional level, and an intellectual level. Hell, to everyone's misfortune, reflects that structure in the same descending order. So the highest level is divided into three portions in exactly the same way that the lowest level is.
Human beings stand in the middle between these two regions. It is actually a battlefield, because a struggle is taking place to claim the human soul for an ascending or a descending force. The battle is like Tolstoy's most famous novel in both scale and nature, because it reflects the dilemma in War and Peace: every player, even the most powerful ones, believes they are in control of their own destiny, but the forces in action are vast in scale and categorically eclipse the ability of any single entity to affect them. This is, in fact, exactly the way that Gurdjieff described universal forces, and perhaps the root origin of his rather grim prognosis for man's chances of affecting his own destiny.
We might note here that the development of the astral body is sensed through the arrival of a new vibration in the cells, which will become relatively permanent if the astral body truly forms the connection it needs. This is because the physical body is the mirror image of the astral body; in other words, there is a specific reason that the "sense" of the astral body is connected to sensation, which is mirrored in sound understanding of the cosmological premises. Studying the enneagram can be useful because it precisely explains such things, which are otherwise puzzling or obscure and may be subject to pointlessly superstitious explanations.
In like manner, the development of the mental and the causal body create corresponding increases in the rate of vibration of the emotions and the intellect. The development of the astral body will inevitably lead to the beginning of an understanding of this question; but until that happens, the question remains relatively mysterious.
May your soul be filled with light.