The quote you're wondering about, "Doctors can heal the body, but it is music that uplifts the spirit," isn't particularly complex, it seems to me. We all understand, I think, that we are comprised of more than just our physical bodies. We also have spirits and emotions and a soul. Research has also shown that there is a general correlation between the condition of the soul and spirit and the condition of the body. If one is sick, the other often exhibits signs of sickness, as well. (I'm a literature teacher, and I can't help but cite Arthur Dimmesdale in The Scarlet Letter as one who demonstrates this perfectly.)
This quote, then, discusses the fact that medicine can cure the body, but the spirit or soul needs something else to keep it healthy and positive. According to this quote, that medicine for the spirit is music. The inference is that an unhealthy body can be healed by medicine, and an unhealthy spirit can be healed by music.