hmmm multiple purposes. Some use to give glory to od, some use it to bring people to God, some use to grow closer to God. The reasons behind why people make and why people listen to Christian are as varied as Christians themselves. I dont think you cn honestly fit it all into one category. If you did I guess it would have to be glorifying God which I think it all does. I mean who are we to judge what is glorifying and what isnt. Everyone glorifies God in there own ways. Whether through hymns and abiding radio or through screaming vocals and heavy metal. I cant imagine God care. Especially consider the Bible says make a joyful noise. It doesnt state make a noise in this certain way....
Music was never designed to be evangelistic, but only for praising God. There is no examples in the NT of music ever been used for evangelism. God has incredibly strict standards in worship, which we see in the Old Testament (which many don't think apply, but does). We're all priests before God and should take the care of seeking out God's standards of worship as meticulously as the Levitical priests did. If God was still in the business of striking people dead for worshipping in profane ways I think 3/4 of the church would be dead because they lack reverence.