I recently fielded a couple of questions about channeling this week, and seeing as channelling versus possessing is a very fine line indeed, I thought it might be useful to share those thoughts publicly.
So that we're all on the same page: a channel is a living being -- usually a human -- who allows non-incarnate beings to inhabit their body and energy to varying degrees. Some channels are temporary (like in a seance, where the medium speaks in the voice of a deceased loved one, or in a ritual where a practitioner channels a god/dess); some are long-term (Amma, for example, is said to be the permanent channel of the Goddess).
"So," you ask, hesitantly. "What's the difference between a channel and a possession?" It's a fine question. The short answer: there is none. Channeling is a form of temporary possession, and whether it become a permanent one comes down to the practitioner, as well as the spirit/s being channeled. The more clear the practitioner is about their own boundaries - as well as their purpose in channeling - the better the probability that the possession will indeed be temporary.
Why is this, you ask? Channels intentionally open themselves up to having beings enter and use their energetic and physical bodies. As suffering beings are opportunistic, it makes channels that much more susceptible to visitations from beings who may not have their best interests in mind.
Beings who walk in the light know that a person's free will is the highest objective. So a being of light would only enter a body if given full permission, and also would be equally willing to leave when the practitioner asked them to.
Where it gets sticky is that there are many types of beings who believe themselves to be evolved (and who, quite frankly, do know a heck of a lot more than humans about creation, evolution and higher spiritual laws) who want a soapbox to speak from...and once they get that, they are loathe to leave it permanently, so they find ways of convincing their hosts to allow for more time. Of course, they can also say that it's in the highest good for them to share their message through their channeler...which seems more ego-driven than guided by the free-will principle.
That said, there are ways to intentionally channel beings for periods of time in ways that can be mutually beneficial. I've also known actors and dancers to "step into the field" of certain personas in order to use them for creative purposes (in fact, my mentor Suzanne Connolly works with actors to accomplish this safely). Again, this all comes down to good boundaries and clear intentions, as well as a healthy sense of who you are.
Finally, a word about possession: all possessions are temporary, no matter how entrenched a being seems. So truly, a possession is NOT THE WORST THING! A being can only stick around if there's permission given. If permission is given consciously, well, there's nothing to be done about that, as it's the individual in question wants the possession. If the permission is unconscious, however, it's coming from wounding...and the good news is that all wounds can be healed, if one is willing to challenge one's "comfortable" (eg, familiar) assumptions about the nature of one's own reality.