Mediumship is the opposite of adeptship; the medium is the passive instrument of foreign influences, the adept actively controls himself and all inferior potencies.
From the above quotation we see immediately that mediumship and adeptship are as opposed as the poles. The medium, to be a success as a medium, must be passive; the more passive he is, the more successful he is as a medium. The moment he begins to exercise and control, that moment he ceases to be a medium. The Adept, on the other hand, actively controls not only himself but "all inferior potencies."
A medium has no will power; he is only a passive agent in the hands of spirits and intelligences of a lower order. These manifest through the medium's own astral spirit and make their presence known by various kinds of phenomena. He can neither command their presence, nor will their absence; can neither compel the performance of any special act nor direct its nature. This is one of the reasons why mediumship is so dangerous. In Isis Unveiled, H. P. Blavatsky tells us that when the medium is perfectly passive "his own astral spirit may be benumbed, and even crowded out of his body, which is then occupied by an elemental, or, what is worse, by a human fiend of the eighth sphere, who proceeds to use it as his own." Too often, she says, the cause of the most celebrated crimes is to be sought in such possessions.
Ill health is another resultant of mediumship; the abnormal tension to which the medium's nervous system is subjected naturally reacts on the physical body. What is worse, mediums are also inclined to vices of various kinds. The moral condition of the medium determines the type of spirits he attracts, and he is reciprocally influenced by them intellectually, physically and morally.
In her article, "Psychic and Noetic Action," H.P.B. gives a rather technical but excellent description of mediumship:
A mediumship is simply one in whose personal Ego, or terrestrial mind (psuche), the percentage of "astral" light so preponderates as to impregnate with it their whole physical constitution. Every organ and cell thereby is attuned, so as to speak, and subjected to an enormous and abnormal tension.
From this we see that the medium has opened the doors of his inner being to the influences of the Astral Light whose "soul is divine, but whose body—the light waves on the lower planes, infernal." It is this "infernal" body to which the medium is attracted, and with whose influence he has allowed every organ and cell in his body to become impregnated.
Theosophy teaches that there can be no communication with the dead once the separation between the lower and higher natures has taken place; therefore what the medium contacts are not the souls of the "dear departed" but the "pale soulless corpses moving in the trackless fields of 'Kama loka.'" So, while Spiritualists may regard mediumship as a privilege and a blessing, Theosophy teaches that it is the very reverse. If the medium knew the true nature of the "beings" he contacts, it would, says H.P.B., strike his heart "cold with horror."
Thus we see that while on the one hand the medium has no control over inferior potencies and is simply a "passive instrument," on the other hand the Adept, who is a pure Magician, an active Mediator, is in complete control over himself and the denizens of the invisible spheres.
Just how complete his control is, is shown in "Psychic and Noetic Action," where H.P.B. says that the Adept can "paralyse at will the memory and the instinctual, independent action of all the material organs and even cells in the body of flesh." Unlike the medium, the Adept is able to maintain perfect mental and physical health, and keep his body, soul and spirit conscious and in perfect harmony.
Thus we see how far apart the medium and the Adept are, for the latter, instead of being controlled, controls all forces with an iron will. He has, in truth, made Nature his "ally, pupil and servant."
Between the two poles of mediumship and adeptship, where do we find ourselves? Neither a medium nor an Adept becomes such in a single incarnation; both have come to be as they are through a long series of incarnations involving many choices.
In "Are Chelas Mediums?" (reprinted in U.L.T. Pamphlet No. 13), we are told that "Every man has his little 'weaknesses,' and every man has his little 'mediumship'; that is to say, some vulnerable point, by which he may be taken unawares." Herein lies our danger. We must be constantly alert and aware of what we are doing, and must overcome our weaknesses instead of giving way to them. Ideas influence us, but those very ideas can be either of love, mercy, generosity, etc., or of greediness, hate, jealousy, or some other passion, and their influence on us can be as powerful as any influence a medium is subjected to.
There are, however, two kinds of influences at work on us, the lower and the higher, the psychic and the noetic—the first leading in lives to come to mediumship; the latter, to chelaship and adeptship. The chela also has put himself under the influence of another being, but that "other being" is one of those exalted men called Mahatmas. It would be an error to call a chela a medium because, rather than being a passive instrument, he is learning to control himself and all "inferior potencies." His is a voluntary and conscious choice.
The choice, therefore, lies with us—whether we shall do as the Adept has done and gravitate towards the "soul" of the Astral Light, or shall fall under the influence of its "infernal body." Alertness and awareness are needed to attain the former and avoid the latter. While we are not as yet in a position to control the Astral Light, we can acquire a theoretical knowledge of it, to begin with, and then when the time comes, know the practical art of dealing with it. In the words of H.P.B.:
Blessed is he who has acquainted himself with the dual powers at work in the ASTRAL Light; thrice blessed he who has learned to discern the Noetic from the Psychic action of the "Double-Faced" God in him, and who knows the potency of his own Spirit—or "Soul Dynamics."