What makes music Spiritual or Christian?

For avowedly Christian music it [the music of Pärt] is not, perhaps, very plainly founded upon the Incarnation of the Son of God. Dale Nelson

I've been thinking again about an episode a few years ago when some Arvo Pärt music was used because he was a Christian. Pärt's music has a sense of silence, of stillness and therefore of course can provide a setting but dangerously this can be merely utilitarian muzak like elevator or supermarket background music. I read an interesting article which contrasted Bach and Part. Bach wrote, “In a reverent performance of music God is always present with His grace” however his understanding is very much a verbal one. Yet perhaps the key observation from Dale Nelson is Bach wrote music for the church, while Pärt mostly writes for the concert hall. Very different contexts and very different reasons for writing.

Much of modern contemporary worship is performative rather unitive. Performed from the front and self-reflective there a danger of the personal worship album as a collection of personal songs is being used supposedly to unite people. What was the reason for writing the song and what was the setting intended?

I read that CS Lewis once heard a Zulu war song and thought it was “wistful and gentle” and consequently wondered whether music was really a universal language. However when we use music we should use it self-consciously making clear theological decisions. Why are we using this? Are we using it with some sense of integrity and understanding or merely as wallpaper?