Power
Walking into New York City's Le Cirque without a reservation (that probably should have been made a year ago) and exclaiming (with emphasis) you're a music therapist from Central Falls, Rhode Island, and would like a table for four promptly probably won't do anything for you except get you thrown out by a snotty (but probably good-looking) maître d'.
And, unlike mail carriers, who claim that "neither snow, nor rain, nor gloom of night, nor the winds of change, nor a nation challenged" will stay them from the swift completion of their appointed rounds, it's possible that your appointed rounds may be stayed by a bad case of the flu, a root canal appointment, or even (gasp) just the need for a day off. There is no "music therapist creed" per se; you'll just have to make one up for yourself, if this music therapy career is something you feel compelled to do.
That being said, the power you do get from being a music therapist will likely come directly from your patients and their families. And that, friend, is a lot of power. (More power than that out-of-work-actor playing maître d' at a famous restaurant can provide you anyway.)
Power to know you're doing some good and power to know you're helping someone is power to help you sleep well at night (even if you're in a fourth story walk-up with no air conditioning during the hottest summer on record).
"Power" coming from unreliable sources is sometimes fleeting. Just ask Rupert Murdoch.