This subject, about the causal body, opens up for the thinker much food for speculation. The literal figures and the dimensional lines cannot be given. They form one of the secrets of initiation but certain ideas may be suggested and submitted to the consideration of all interested.
Just what do you mean when you speak of the causal body? Say not glibly, the body of causes, for words thus spoken are oft but nebulous and vague. Let us now consider the causal body and find out its component parts.
On the involutionary path you have what is termed the Group Soul, aptly described (as far as earth words permit) as a collection of triads, enclosed in a triple envelop of monadic essence. On the evolutionary path, groups of causal bodies correspond and are similarly composed, three factors entering in.
The causal body is a collection of permanent atoms, three in all, enclosed in an envelop of mental essence… What happens at the moment when animal-man becomes a thinking entity, a human being? The approximation of the self and the not-self by means of mind, for man is “that being in whom highest spirit and lowest matter are linked together by intelligence.” What do I mean by this phrase? Just this: that when animal-man had reached a point of adequacy; when his physical body was sufficiently co-ordinated, when he had an emotional or desire nature sufficiently strong to form a basis for existence, and to guide it by means of instinct, and when the germ of mentality was sufficiently implanted to have donated the instinctive memory and correlation of ideas that can be seen in the average domesticated animal, then the descending Spirit (which had taken to itself an atom on the mental plane) judged the time ripe for taking possession of the lower vehicles. The Lords of the Flame were called in and they effected the transfer of polarization from the lower atom of the Triad to the lowest atom of the Personality. Even then, the indwelling Flame could come no lower than the third sub-plane of the mental plane. There the two met and became one and the causal body was formed. All in nature is interdependent, and the indwelling Thinker cannot control in the three lower worlds without the aid of the lower self. The life of the first Logos must be blended with that of the second Logos and based on the activity of the third Logos.
Therefore, you have at the moment of individualization, which is the term used to express this hour of contact, on the third sub-plane of the mental plane a point of light, enclosing three atoms, and itself enclosed in a sheath of mental matter. The work then to be done consists of:
- Causing that point of light to become a flame, by steadily fanning the spark and feeding the fire.
- Causing the causal body to grow and expand from being a colorless ovoid, holding the Ego like a yolk within the egg-shell, to a thing of rare beauty, containing within itself all the color of the rainbow. This is an occult fact. The causal body will palpitate in due course of time with an inner irradiation, and an inner glowing flame that will gradually work its way from the center to the periphery. It will then pierce through that periphery, using the body (that product of millennia of lives of pain and endeavor) as fuel for its flames. It will burn all up, it will mount upward to the Triad, and (becoming one with that Triad) will be re-absorbed into the spiritual consciousness, – will carry with it – using heat as the symbol – an intensity of heat or quality of color or vibration that before were lacking.
Therefore the work of the Personality – for we have to view all from that angle until egoic vision may be ours, – is first to beautify, build and expand the causal body; secondly to withdraw within it the life of the Personality, sucking the good out of the personal life and storing it in the body of the Ego. We might term this the Divine Vampirism, for always evil is but the other side of good. Then, having accomplished this, comes the application of the flame to the causal body itself and the joyous standing by whilst the work of destruction goes on, and the Flame – the live inner man and the spirit of divine life – is set free and mounts to its source.
The specific gravity of the causal body fixes the moment of emancipation and marks the time when the work of beautifying and building is completed, when the  Temple of Solomon is erected, and when the weight (occultly understood) of the causal body measures up to the standard looked for by the Hierarchy. Then the work of destruction supervenes and liberation approaches. Spring has been experienced, the full verdure of summer has succeeded, now must be felt the disintegrating force of autumn, – only this time it is felt and applied on mental levels and not on physical. The axe is laid to the root of the tree, but the life essence is garnered into the divine storehouse.
The content of the causal body is the accumulation by slow and gradual process of the good in each life. The building proceeds slowly at first, but towards the end of incarnation, – on the Probationary Path and on the Path of Initiation – the work proceeds rapidly. The structure has been reared, and each stone quarried in the personal life. On the Path, in each of its two divisions, the work of completing and beautifying the Temple proceeds with greater rapidity…
(Letters on Occult meditation – Alice Bailey)