Celtic Church

The Celtic Church is a semi-mythical, quasi-historical quasi-entity, which existed in north-west Europe in the latter half of the first millennium CE. Because the Celts function as a kind of "indigenous"/"tribal" proxy for people of European origin, wooly thinkers frequently associate them with urban fantasies about nature and primitive life. And the Celtic Church/Christianity guff out there reflects this.

Fantasy
Some popular misconceptions:
 * The Celtic Church was a New Age before its time, full of druids, who loved plants and animals, and the great outdoors.
 * Galatians good, Romans bad.
 * It was an independent church, theologically uncontaminated by Rome, Alexandria, etc.
 * All of its prayers were in English (and some were unheard of before the 19th and 20th centuries).
 * Christian Celts liked synthesisers and harps in their music.
 * They worshipped rocks.
 * They didn't make war.

Basically all of this is design serves to make anti-Catholicism, pantheism and New Agey-ness a little more palatable to a middle-class Christian audience.

Reality
Contrary to popular belief, Celtic Christianity was not a separate entity from the Roman Catholic Church at all, just a somewhat detached portion, that ended up getting cut off from Rome and Constantinople by a series of Germanic invasions and population movements in northern Europe. As a result, Celtic Christians developed some idiosyncrasies such as hereditary abbots, funny tonsures, and their own way of calculating the date of Easter. The discrepancies got sorted out at the Synod of Whitby in 664 CE, when the Vatican's caucus basically bullied its way into "correcting" many of these "errors".

A few genuine facts about the Celtic church:
 * It produced wonderful manuscripts. Some of the best illuminated works of Western Europe including the Book of Kells and the Lindisfarne Gospels came out of this tradition.
 * It had a lot of saints. And we mean a lot. Some of them you'll never have heard of, guaranteed.
 * Some of the Celtic saints are Christianized versions of ancient Celtic gods such as Bride/Bridget, but this was not unusual at the time. The Celtic Church was not that much more "pagan" than many of the other tendencies in Christendom.
 * Some of their churchmen such as St. Columba were actually warriors and statesmen, rather than pacifists.
 * They helped [re-]Christianize England (especially the North) and set up educational institutions in many parts of Europe.
 * None of them wrote cute prayers in flowery English. Some of its members could speak Anglo-Saxon though.
 * They loved being hermits, and living on small islands. That part is true.
 * Their clergymen could marry. Many Scottish and Irish surnames have ecclesiastical origins e.g. MacNab, MacPherson, Haggarty etc. Note, however, that married clergy were also not unusual at the time; married priests in the Latin Church, while officially forbidden, were generally tolerated until the eleventh century.

In the end, the Reformation destroyed many Celtic church traditions for good, particularly in Scotland, Wales and Cornwall.