The Restoration Movement is the product the merger of two earlier movements, one founded by (among others) Barton W. Stone in Illinois and one founded by Thomas Campbell in western Pennsylvania. Both men were defrocked Presbyterian ministers, expelled from their denomination for treating believers outside their denomination (or sect within Presbyterianism) as brothers in Christ.
Soon many towns had churches of both stripes, and yet they were similar (not identical) in their preaching. By this time also, Alexander Campbell had become the leader of the Campbell-movement (“Reformer”) churches, working among the Baptists to unite across denominational and doctrinal lines based on confession of Jesus as Messiah and submission to baptism — and nothing more.
In 1832, the two congregations in Lexington, Kentucky famously merged at the behest of leaders of both movements — although Alexander Campbell was initially reluctant to bless the merging of the movements. But he quickly came to endorse the idea, and congregations across the American frontier merged.
To encourage the mergers, Campbell asked Stone to consolidate the hymnal his churches were using (and that Stone was publishing) with Campbell’s hymnal, the profits to be dedicated to educating new ministers.
In Campbell’s day (first half of 19th Century) instrumental music was not controversial. The small frontier churches couldn’t have afforded a piano even if they’d wanted one, and nearly every convert was from a Calvinist denomination — either Presbyterian or Baptist. Hence, although Campbell and Stone had rejected the salvation theology (soteriology) of Calvinism, they kept the RPW and so rejected instruments in principle — although neither made the RPW or instruments a fellowship or salvation issue.
Campbell famously said,
So to those who have no real devotion or spirituality in them, and whose animal nature flags under the oppression of church service, I think with Mr. G., that instrumental music would be not only a desideratum [something to be desired], but an essential prerequisite to fire up their souls, to even animal devotion. But I presume, to all spiritually-minded Christians such aids would be as a cow bell in a concert.
Alexander Campbell, “Instrumental Music,” Millennial Harbinger, Fourth Series, Vol. I., No. 10 (October, 1851), pp. 581, 582.
This is well known in Church of Christ circles. Less well known is,
I would prefer to have an organ, or a fashionable choir as a means of my worship than the words of a hymn set to the notes of a tune on which to fix my eyes while engaged in the worship of God.
Alexander Campbell, “The Christian Psalmist,” Millennial Harbinger [March 1847], p. 179 [quotation is thanks to Bobby Valentine].
Campbell’s hymnal had no notes — which was not unheard of in his day, but the practice was already antiquated as church members wanted the notes to help them sing. But Campbell considered the presence of notes in a hymnbook worse than instrumental music!
So the mindset created by the extra-biblical RPW led not only to the rejection of printed prayers and instruments of music, but made the presence of notes in a hymnal worse than a choir or organ.
The peculiarities in the RPW also show up in Campbell’s opposition to singing classes at church. Jim Mankin, “Alexander Campbell’s Contribution to Hymnody,” 49, No. 1, The Hymn , p. 13. Where do we find authority for singing classes in scripture?
After Campbell’s death, whether to include notes in future editions of his hymnal was something of (yet another) controversy. But as we all know, it didn’t take long for publishers to provide not only notes for melodies but also four-part harmonies and shaped notes to facilitate sight singing — meaning that Luther won out even in the Churches of Christ. It just took 500 years.
Before his death, Campbell helped found the American Christian Missionary Society, and it took over publication of the Movement’s hymnals after Campbell’s death. In 1870, a tune book was produced for use with the Society’s hymnbook. The next year, the Society published an alternative volume with both words and music, The Christian Hymnal. So the Churches of Christ have been singing from hymnbooks with notes for only about 145 years. This was obviously an “innovation,” but one we were glad to see happen. It appears that even the Sommerites, who split over instrumental music, missionary societies, bake sales, and located preachers, were pleased to finally get the notes.
Beginning in the late 19th Century, hymnals in the Churches of Christ were produced by private companies. After all, the a cappella churches largely also rejected the missionary society, and so weren’t about to buy their hymnals. Until 1923, the Gospel Advocate published a hymnal produced by members of both instrumental and a cappella churches. Beginning that year, the hymnals were edited exclusively by members of a cappella churches.
Now, I grew up in a small Church of Christ in north Alabama — and we had (and were helped by) singing classes. Our hymnals had four-part harmony notations with shaped notes. And in our part of town, the RPW damned those who used an instrument but approved notes and singing classes — contrary to the teachings of Campbell. And our weddings came straight out of the Book of Common Prayer (the preacher kept a copy in his office for just this purpose) even though a wedding could not have instrumental music because it was too much like a worship service, as weddings involved a church building, preacher, prayer, and suits.
In other words, you could more easily predict whether a practice might violate the RPW with a pair of dice than any amount of Bible study. The results of the RPW were (and are) entirely subjective, driven more by traditionalism and a desire to damn those in other denominations than any truly rigorous principles. After all, the line between an “act of worship,” an “aid,” an “addition,” or an “expedient” is very much in the eye of the beholder.
 Baptists were Calvinist before the Civil War, but most Southern Baptists today are not — except for their insistence on the perseverance of the saints. John Piper is leading a resurgence of Calvinist thought among Baptists, but Calvinism remains a minority position today. It was the majority position in the first half of the 19th Century, as the Baptists took their theology, other than regarding baptism, from the Puritans.