I've rejected the label "Christian musician." Christians are people. Music cannot be Christian or not Christian any more than it can be the color purple or not. Music is music.
I can’t speak for the purpose of other people’s music, but for us we make music to express and open the human heart. Music helps me to more fully experience the transcendence and magic of existence.
I have found that if I make music that first helps me experience something personally, it often has the same effect in others as well. I prefer that to primarily trying to accomplish a “purpose” in someone else.