- It can be beautiful. It can also be cacaphonic (in terms of sound, the equivalent of "catastrophic"), which is also true of accompanied vocal music and solely-instrumental music. (Think sixth-grade band.) We don't forbid tone-deaf people from singing, since God hears the heart as well as the voice.
- It has a quality of purity and emotion. Vocal music comes from the heart. I don't play an instrument, but I have heard instrumental music performed by virtuosos from Van Cliburn to Louis Armstrong to Yo Yo Ma that convinces me the same thing can be said of it.
- It can put praise into words. This is the advantage a cappella music has had for generations. However, it is no longer a unique advantage. With the development of electronic synthesizers - both instrumental and vocal - it is possible for an artificial instrument to "sing" as a proxy for those who have no voice. Wouldn't it be a crime to deny that blessing to those folks, just because their voice is not generated by vocal cords, tongues and lips?
- It has always been at the heart of the word "sing." At the same time, it has not been exclusively the concept behind singing since Adam's eighth-generation descendant Jubal, "the father of all who play the harp and flute" (Genesis 4:21). Some music is written to be sung a cappella. Some music is written to be sung accompanied. Some music is written to be performed on instruments. Sometimes, these kinds of music can be arranged for a different kind of presentation. Sometimes that works well; sometimes it doesn't.
- It is not forbidden in scripture. It is also not authorized or commanded in scripture. Many Old Testament passages encourage singing praise with instruments. And God chose to share a Revelation with John of a panorama of heaven where praise takes place with harps in hand (15:2-3) and cosmic events are heralded by trumpets (8:1ff).
- It is probably exemplified in scripture. (By implication. It's pretty hard to sneak instruments into a jail and play them when your hands are in shackles. This account - Acts 16:25 - also exemplifies worship outside of the normal gathered worship, and says nothing about what day of the week Paul and Silas were imprisoned.)
- It is natural. Children sing when they are happy. They don't have to be told to do so. They also make rhythm instruments out of whatever is available. (Teenaged males are especially fond of imitating drums.) And God creates praise through His own creativity. He hears song in the mountains and hills; the clapping of hands in the trees (Isaiah 55:12) and the rivers (Psalm 98:8). He accepts praise from all creation: sun, moon, stars, heavens, clouds, sea creatures, wild and domestic animals, birds, kings, princes, young people and old (Psalm 148). He speaks in thunder (Job 37:4; Psalm 18:13; John 12:29; Revelation 10:4). All of these sources of praise are natural - but not all of them come from vocal cords, tongues and lips.
- Some church fathers preferred it. Several of them - one or two of them, fairly early on in church history. They had their expressed reasons: to many of them, instrumental worship smacked too much of pagan worship. The Jewish-ness of the early church was giving way to the Gentile-ness of its growing base. While Jewish Christians might have associated instrumental praise with King David, psalms and temple worship, Gentile Christians were more likely to have connected it with raucous and raunchy pagan ceremonies. I understand their preference. I respect it. It still doesn't carry the weight of inspired scripture to me. Their teachings are teachings of men, whatever their motivation or reasoning. To be valid preferences today, the same conditions would have to exist, producing the same reasons. Contemporary Christian Music gives ample evidence that praise can still be performed instrumentally as well as vocally in the culture I'm in, and probably many others as well.
- I like it. I really do. I worship and work at a church which performs a cappella worship before the Lord, exclusively. I can queue up almost a whole day's worth of ZOE Group on the iTunes of the G5 Mac in my office and be blessed with no need of any other kind of music. (There are days when I do!) It's not the only kind of music I like. And it's not the only kind of worship music that I like, and believe to have always been acceptable before God.
A cappella-only worship or instrumentally-accompanied worship are matters of opinion, often based on personal preference and certainly based on interpretation of scripture rather than scripture itself. And where matters of opinion regarding worship and Christian living come into play, the guiding principles are found in Romans 14. These are disputable matters; matters of conscience. It would be just as wrong for an a cappella-only advocate to worship with instrumental accompaniment as it would be for me to condemn that person for calling unclean what I believe God has never called unclean. Both of us would be violating our consciences. We can disagree on this matter. We can still serve and worship God within our consciences intact and please Him. But we cannot please Him by going beyond what His word says, turning our preferences into doctrines attributed to Him, or judging and condemning others for violating our own doctrines-of-conscience.
These are all the things I can say about a cappella music and worship. There are a lot of things I can't say, because they aren't in scripture, rooted in scripture, or rooted in the unchanging nature of God. So it's just best not to say them, isn't it?
I write this while listening to my iPhone app "Ambiance," specifically the "Large Wind Chime" (possibly recorded at the world's largest tuned windchime in Eureka Springs, AR?). It is beautiful and haunting and awe-inspiring music, and if you think about it, powered by the wind at God's whim. It's the sound of God playing a musical instrument made by man.