The fact God has specified in the New Testament ways in which we are to worship him indicates that he still cares about the form of worship, that it is not a matter of indifference to him. If he simply had said “worship me” and not identified ways in which he desires to be worshiped, everyone would agree that all ways of worshiping him would be acceptable. But since he commanded specific ways of worship, one devoted to pleasing him should not risk displeasing him by worshiping in ways he has not commanded.
This seems to be a good and fair statement, from Ashby Camp, in a PDF review of Milton Jones’s work on instrumental music. His review is enlightening.