For each section of the astral body acts strongly upon the corresponding section of the mental body, but only upon the corresponding section; it cannot influence any other part.

So the causal body can be affected only by the three higher portions of the astral body; and the oscillations of those represent only good qualities.
The practical effect of this is that the man can build into the ego (that is, into his true self) nothing but good qualities; the evil qualities which he develops are in their nature transitory and must be thrown aside as he advances, because he has no longer within him matter which can express them.

The difference between the causal bodies of the savage and the saint is that the first is empty and colourless, while the second is full of brilliant, coruscating tints.

As the man passes beyond even saint-hood and becomes a great spiritual power, his causal body increases in size, because it has so much more to express, and it also begins to pour out from itself in all directions powerful rays of living light.

In one who has attained Adeptship this body is of enormous dimensions.
The mental body is built of matter of the four lower subdivisions of the mental world, and expresses the concrete thoughts of the man.