It is uncertain when or how Christianity first arrived at those westernmost reaches. It seems always to have been there. Legend tells us that Irish bards attended the events on Golgotha "in the spirit." In the Celtic tradition there is a continuity in cosmic process. For the Celt, Christ's death and resurrection was a healing that allows a reconciliation between humanity and nature in God. In this sense, Christianity was always in Ireland, and we seek its historical beginning in vain.
If the Celtic Church had survived, perhaps the fissure between Christianity and nature, widening through the centuries, would never have fragmented our Western attitude toward nature and the universe.