Differences Among Spirits
A writer on this subject well says regarding this particular point:
"Some spirits may lack both knowledge and aptitude; others may have the
knowledge, but yet fail from want of the power to control. They may be
able to affect one mediumistic person and not another. Likewise, they
may be able to use a sensitive medium for one phase of mediumship, and
yet be unable to succeed in any other direction. A spirit may be in such
conditions that he can produce good physical phenomena; he may, however,
try to do so through a sensitive who is fitted only for trance or
clairvoyant mediumship, but who does not possess the quality or psychic
force for sensuous manifestations. A medium who is naturally qualified
for physical demonstrations may persist in desiring trance or
inspirational mediumship, and be determined to become a speaker or
nothing.