Romantic Christianity made a brilliant start with Novalis, William Blake and ST Coleridge - and then nothing-much for many decades until Rudolf Steiner became (strange sort of) Christian in about 1898; to be followed by Owen Barfield and William Arkle in later generations - and there is William Wildblood and myself among current writers. But there have never been many Romantic Christians...
Why so rare, and what went wrong with the intermediate generations? Of course there were plenty of Romantics - but among them hardly any Christians; indeed most of them were either atheists or spiritual anything-but Christians.
A pre-eminent example was Ralph Waldo Emerson; who was an arch-Romantic and who began as a Unitarian minister - Unitarians being, at that time, like Emerson, Christians on-the-way-out. He ended-up as a kind of deist, flavoured with what he had gathered of Hinduism and Sufism.
Emerson was known for his elevation of the intuitive, epiphanic, 'moment' of insight to the highest possible valuation; like most Romantics, he required that all knowledge be derived from direct personal experience. SO why did Emerson not do the same for Christianity as he did for everything else? Why did he not develop a Romantic Christianity built from the kind of direct intuitive insights that fuelled the rest of his wide-ranging creativity? This will be answered below.
My guess is that Emerson accepted the evaluation of most Churches that Christianity must be derived from external authority - or else it is not Christianity. Catholics demand that the individual conform to the teaching of the Church authorities, or the traditions of the lineally descended ancient Church. Protestants demand conformity to the canonical scriptures of the Bible.
But what unites all churches is the assumption that whatever Christianity is, it is located outside the individual. The insistence is that Christianity does not come from within - not from individual experience, not from personal intuition.
Ultimately the task for the individual is to conform to external authority. The church judges the individual.
If this is true; then Romanticism and Christianity are incompatible. So, how did Novalis, Blake and Coleridge come to believe that they had developed a Christianity based on their inner knowledge? It is mostly a matter of their basic and ultimate assumptions, of metaphysical assumptions. These authors believed that the individual could have direct knowledge of Christianity without it being derived from any intermediary at all; not rooted in church authority, without canonical scripture, traditional, philosophical theology or anything else.
Or, at least, and in conformity to Romanticism; that this direct form of personal knowing should serve to evaluate all other knowledge claims. So the individual judges the church; and may (like Blake, Steiner and Arkle) dispense with all churches - although Coleridge and Barfield were both, in later life,' communicating' (communion-taking) members of the Church of England.
We can see, then, why Emerson did not remain a Christian - because he apparently accepted the assertion that a real Christian must be under the authority of a church. (The only dispute was about which church/es it was correct to regard as really Christian.) It seems that, for Emerson, anyone who claimed to be a Christian outside of a church, was not really a Christian.
But there may be more to it than this - because Emerson did not believe in the divinity of Jesus; therefore real Christians were in error. Emerson's idea of deity was abstract - 'The Over Soul' - and therefore infinitely different-from a Man. The only union of Man with deity, therefore, was for Man to surrender his self and 'melt-into' the infinitude of deity.
So Emerson was a hopeless case! Ultimately, he did not want what Jesus offered; and preferred what Eastern religions offered. And what applies to Emerson, also applies to many other Romantics since. Some Romantics are materialist; but among those who are spiritual - it has mostly been an Eastern spirituality; which ultimately regards the individual self and our mortal world as temporary illusions.
This is the source of the paradox by which Emerson valued the moment of insight above all; yet ultimately he regarded each epiphany as evanescent, soon to be lost in time - and therefore worthless.
Other Christians have had strong Romantic impulses, but retained the conviction that the individual judgement must be subordinated to church authority - GK Chesterton is an example. Chesterton regarded the 'catholic' church (at first the Anglo Catholic wing of the Church of England; then in his late middle age, the Roman Catholic church) as the source of knowledge, of truth. For Chesterton Romanticism was the proper attitude each individual ought to adopt towards this truth.
For Chesterton, therefore, the individual did not have direct and personal intuitive access to knowledge; except for the knowledge that the church was true. The only primary knowledge was that the church was the only source of knowledge.
Something similar could be said for CS Lewis and JRR Tolkien. They were Romantics and also Christians - but their Romanticism was secondary to their Christianity - and was at most understood to be a good and proper (perhaps even necessary) attitude towards their Christianity. The Romantic intuition was not, for them, a primary source of knowledge: that was revelation as communicated by their churches.
This is why Romantic Christians - by a strict definition - have been so rare. Most Romantics were not Christians, but among those that were; Romanticism is regarded as an attitude but not as a source of knowledge.
It was the great contribution of Owen Barfield - posthumous disciple of Steiner, best friend of CS Lewis, and fellow Inkling with Tolkien - to clarify and emphasise this vital distinction.