Tullian Tchividjian gives a good answer. The entire post is here.
You see, when we separate people according to something as trivial as musical preferences, we evidence a fundamental failure to comprehend the heart of the gospel. We’re not only feeding toxic tribalism; we’re also saying the gospel can’t successfully bring these two different groups together. It’s a declaration of doubt about the unifying power of God’s gospel. Generational appeal in worship is an admission that the gospel is powerless to join together what man has separated.
In Paul’s day the world was rigidly divided between Jew and Gentile, slave and free, male and female. Those walls of separation were thick, and the groups on each side were hostile. But that didn’t stop Paul from boldly proclaiming God’s intention to establish a new community—the church—that not only included all these but also allowed them to enjoy deeply interdependent relationships. As Paul argued for the Gentiles’ place in God’s redemptive plan, he said, “There is no distinction between Jew and Greek; for the same Lord is Lord of all, abounding in riches for all who call upon him” (Romans 10:12). As Paul decried certain Jewish leaders for teaching that the sign of circumcision was a condition for justification, he wrote, “There is neither Jew nor Greek, there is neither slave nor free man, there is neither male nor female; for you are all one in Christ Jesus” (Galatians 3:28). And when he addressed class distinctions threatening to divide the church, he asserted our newness in Christ, in which “there is no distinction between Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave and freeman, but Christ is all, and in all” (Colossians 3:11). If he were writing to the 21st Century church you could almost hear him say, “There is neither ‘traditional’ nor ‘contemporary’ worship; for you are all one in Christ Jesus.”
The primary reason, though, that stylistic segregation in worship shrinks our souls is because it prevents us from knowing God deeply. The only way to know him deeply is to have many different types of Christian people in your life, since each person will help to reveal a part of God that you can’t see by yourself. This means the great tragedy of segregation isn’t so much that we see less of each other but that in separating from each other we see less of God. All of us need other lights than our own to see more of his myriad facets.
So, we miss out on some great things God intends for us to enjoy when we separate in worship according to musical tastes. The idea to do this comes, not from the Bible, but from American consumerism and we adopt this practice to our own peril.
As my friend Steven Phillips rightly says, we ought to use the best music, prayers, and traditions of our Christian past, so that our worship is guided and enriched by our fathers in the faith. In doing this we demonstrate that our Christian faith reaches back thousands of years. And we ought also to use the best new songs and styles – to “sing a new song to the Lord” as the Psalms say – so that we can demonstrate that the grace of God is ever new. God’s saving power is available now, in the present day, to all who call on Him in faith.
By musically blending things in this way we exercise love toward those who resonate with different musical tastes than us. We recognize that our worship service is a shared time and a shared space, so that if a particular song or style doesn’t inspire us, we can still look across the sanctuary and give thanks from our hearts for the diversity of people who are here. The gospel of Jesus Christ invites us to look across the aisle and say, “Though this song or style may not appeal to me, I see that God is using it to move you. I love you in Christ and I’m glad you’re here.”