If Michael is truly a non-physical presence, then it goes that they need human "channels" as a means to communicate their information, perspective, and teaching to those of us within the physical plane.
"Channels" are people who have apparently made an Agreement as part of their life plan to act as a voice or energy conduit for non-physical sources of inspiration, healing, or information, that originates from a non-physical consciousness. Most of the time these Agreements are made between the channel and entity before the channel is born, but sometimes a person will make the Agreement later in his or her life.
If this all seems strange, that's because it is strange. It may help to think of "channeling" as just some form of misunderstood creativity, and that "Michael" is just some brilliant part of the "channel's" brain that functions in ways we do not understand, yet.
I don't pretend to know exactly why or technically how channeling is possible, or whether it is valid as we have come to understand it. I do know that something profound is happening and only personal experience can "prove" something like this to you. My own experiences over the years have convinced me of two things:
1. that there is something definitely happening beyond my apparent, daily consciousness that is legitimately being accessed for detailed, expansive, seemingly unlimited and original information
2. and that the information has an obvious, positive impact on me and other students. Those two factors make it worth my efforts to continue exploring and trusting the process, even if I struggle daily with the questions of its validity.
If consciousness does exist beyond the Physical Plane after death, then "channels" are like radio receivers who tune out from their own "soul station" for periods of time to "receive and broadcast" other sources.
"Michael" happens to be a group of souls who have completed their journey through the Physical Plane, speaking as one voice, sharing their wisdom as gained from the many lifetimes of experiences collected by all of the members of that entity.
The channeling I do is limited to my contact with Michael, rather than communicating with an individual who is between lives trying to contact a loved one, though it is true that I do experience contact with many who have died.
Similar to other non-physical teachers, such as Seth, Emmanuel, Lazaris, Orin & DaBen, Michael shares the knowledge and experience they gained while living physical lives, except, of course, now they have a broader/higher perspective.
Michael helps us to understand the dynamics of who we are, both as Personality and as a Soul (Essence), including how to better use the unlimited tools available for understanding, nurturing, and building our selves, relationships, and universe.