No route into the soul is more open than the ears. Once rhythms and modes get in that way, they stamp their own character on the listener and make the soul resemble them. So the kind of music people hear is a moral matter, not just a matter of taste.
Music comes in three kinds. One is the unheard order of the heavens. One is the harmony that holds body and soul together within a person. The third is the audible music of voices and instruments. On this view, what we hear is only the smallest and lowest case of a harmony that runs through the whole universe and through each human being.
The intervals that sound sweetest together, the octave, the fifth and the fourth, are explained by simple whole-number ratios. That turns what the ear enjoys into something that can be measured and proved. Music becomes a branch of mathematics, studied next to arithmetic as training for philosophy.