In one step, from the medieval to Modernism.
The Western Conference Unitarians -- think of the middle third of the United States a hundred and more years ago -- were known for a kind of bibical rationalism and a minimalist style of worship sometimes known as "fiddle and lecture". And I've been looking for some simplified options.
Without directions, it's hard to know what exactly this kind of worship looked like. Yesterday I found a piece of ephemera: an order of service from Jenkin Lloyd Jones's All Souls Church in Chicago, from January 27, 1907. That should be a representative sample from one of that movement's leading lights, maturely developed.
I. Organ Prelude.
II. Voluntary (with "From all that dwell below the skies…")
IV. Choral response.
V. "Prayer, 'Our Father,' chanted."
VI. Scripture.VII. Hymn.
XIII. Organ Postlude.
XIV. Social Greeting.
I can confirm that the hymns map back to Unity Hymns and Chorales, so the "Choral reponse" was surely one from that book, too.
What strikes me is how little congregational repsonse there is. Little, perhaps nothing spoken in the pews -- only hymns and chanting. Perhaps a small step from the Middle Ages, when the silent congregants would look devotionally upon the sacrament: here, the preaching.
Theological qualms aside, such a service can be sensible, even wholesome and devout in a large congregation -- not unknown to "the Unity men." In small congregations, the effect would surely be stilted, and with an unsteady preacher, deathly.
I'll keep looking.