The power of the singing voice
Singing is the most powerful, for singing is living. It is prana. The voice of life itself. No doubt it is also life that is working through an instrument by the touch, but in singing it is the direct life, the breath touching the heart of the listener. However, behind this voice there must be a heart, charged like a battery with what is needed. With what is it charged? With what we call love and sympathy, the greatest power there is.
The healing power of music, p. 282. The inner nature and effects of sound.