St. John's Gospel was an important influence on the early Celtic Christians. He was the disciple they most related to. The best explanation I've found is in J. Philip Newell's Listening for the Heartbeat of God. From page 97:
"John's way of seeing makes room for an open encounter with the Light of life wherever it is to be found. As the history of Celtic spirituality shows, it is a tradition that can stand free of the four walls of the Church, for the sanctuary of God is not separate from but contained within the whole of creation."
(Newell goes on to talk about the tradition of Peter, and how it is equally important. However the two traditions clashed at the Synod of Whitby in 664AD, and the Celtic beliefs and preferences were pushed to the fringes of civilization. It's an important discussion and should not be missed.)
I'm a newcomer to church history, so all this fascinates me. In Shirley Toulson's The Celtic Year, A Celebration of Celtic Christians, Saints, Sites, and Festivals, she writes on page 137:
"Nowadays we celebrate the feast of St. John the Evangelist on 27December, but until the late Middle Ages his festival was also kept on 6 May, and it seems fitting that we should remember the writer whose words were a glorification of the 'light that darkness could not overpower' during the months of the longest days...John's gospel, written at Ephesus toward the end of the first century, is deeply imbued with Jewish ritual and custom. This affinity would have appealed to the Celtic mind, for the nomadic Israelites, like the tribal Celts, realized God's presence in all creation and had prayers for every occasion..."As I mentioned in my last post, it's the season of Beltaine, the light half of the year, and that's what got me thinking about John. Your thoughts???