And here it is:
Celtic Christianity or Insular Christianity refers broadly to certain features of Christianity that were common, or held to be common, across the Celtic-speaking world during the Early Middle Ages. “Celtic Christianity” has been conceived of with differing levels of specificity: some writers have thought of it as a distinct “Celtic Church” of Chalcedonian Christianity uniting the Celtic peoples and distinguishing them from what would become the Roman Catholic Church after the Great Schism, while others classify it as simply a set of distinctive practices occurring in those areas. Scholars now reject the former notion, but note that there were certain traditions and practices used in both the Irish and British churches but not in the wider Christian world. These include a distinctive system for determining the dating of Easter, a style of monastic tonsure, a unique system of penance, and the popularity of going into “exile for Christ”. Additionally, there were other practices that developed in certain parts of Britain or Ireland, but which are not known to have spread beyond a particular region. The term therefore denotes regional practices among the insular churches and their associates, rather than actual theological differences.
The term “Celtic Church” is deprecated by many historians as it implies a unified and identifiable entity entirely separate from the mainstream of Western Christendom. Others prefer the term “Insular Christianity”. As Patrick Wormald explained, “One of the common misconceptions is that there was a ‘Roman Church’ to which the ‘Celtic’ was nationally opposed.” In German, the term “Iroschottisch” is used, with Lutz von Padberg placing the same caveat about a supposed dichotomy between Irish-Scottish and Roman Christianity. Celtic-speaking areas were part of Latin Christendom as a whole at a time in which there was significant regional variation of liturgy and structure with a general collective veneration of the Bishop of Rome that was no less intense in Celtic areas.
Nonetheless, it is possible to talk about the development and spread of distinctive traditions, especially in the sixth and seventh centuries. Some elements may have been introduced to Ireland by the Briton Saint Patrick, later others spread from Ireland to Britain with the Irish missions of Saint Columba. The histories of the Irish, Welsh, Scots, Breton, Cornish, and Manx Churches diverge significantly after the eighth century (resulting in a great difference between even rival Irish traditions). Later interest in the subject has led to a series of “Celtic Christian revival” movements, which have shaped popular perceptions of the Celts and their religious practices.