Why Music?
http://tolkienmedievalandmodern.blogspot.com/2014/04/why-music.html
As we discussed in class, Tolkien did not invent the idea of music occurring during the creation of the world but rather drew on medieval and biblical sources. In the Job version of creation, the stars sang and the angels shouted.
I think that Tolkien uses music in Ainulindalë because its physical properties allow for it to exist and be described in particular ways within the story and because it fits within the ideas of the medieval philosophers of our primary reality.
Pythagoras and Music of the Spheres
https://www.sacred-texts.com/eso/sta/sta19.htm