Because if you're angry or upset, often that anger will be transmitted into the music. Dr. John Diamond, an Australian M.D., has tested music's healing powers for over 35 years. Something else is transmitted with the music. In other words, whatever mood or state of mind the musician is in when he plays is transmitted to you with the music . When your mind, body, emotions and spirit are aligned, something remarkable happens.
Music can either enhance or disrupt that flow.
In ancient times, the Greeks used music for healing, insights, and clarity.