Didn't King David play the harp?:
Yes he did. He also sacrificed animals for forgiveness of his sins. When Christ died on the cross, the old covenant died with him. We get our pattern for the church & for worship from the New Testament. In the New Testament, there is no example or command given for instrumental music in an assembly. Some people think its overkill, but we try to follow the New Testament example to the best of our abilities.