Orthodox Church history will acknowledge that there are (broadly speaking) two streams in Christianity up until the Great Schism of 1054 A.D.: the Petrine Church (derived from St. Peter and the centralized authority in Rome) and the Johannine Church (derived from St. John the Beloved and the original more mystical and Gnostic Apostolic/Magdalene Holy See of Antioch, which predates the Roman). It is from the Johannine Stream that the Cathars and the Templars came.
The threat of the decentralized mystical spiritual culture which flourished in the Languedoc region of France - a culture of troubadours and higher expressions of love - ultimately was intolerable to Rome, resulting in the horrors of the so-called Albigensian Crusade in the 13th century, which wiped out the Cathars and gave rise to 500 years of torture and extermination of earth-centered spirituality (particularly women who practiced healing wisdom) under the Inquisition.
The takedown of the Templars followed quickly upon the Cathar genocide, setting a template for the genocide of the peoples of the Americas, under the heinously absurd "Doctrine of Discovery" by which the Pope sanctioned the dehumanization of the tribes.
Sustainable, decentralized, earth-centered cultures were and are and shall always be the targets of extermination by oligarchies, whom we may broadly label "those motivated by narrow self-gratification" who aim at destroying the sovereignty of the soul in direct communion with Source, and the sovereignty of the tribe in direct reverent communion with our Mother Earth. Cut this cord of communion, destroy the family unit, and the individual is then dependent upon the state - which is, of course, controlled by the oligarchy as an extension of their agenda.
The story of Ireland and St. Patrick comes down to us as an echo of this pattern. Miraculously, the Celtic spirit survived him, and is alive today as the Goddess arises in Sacred Union with the Universal Christ.
There is an Origin Story told by the Celts of how an Egyptian/Hebrew Princess Scoti (sometimes called Princess Tea and said to be of the Tribe of Dan) fled from persecution around 500 B.C. and came to Ireland, where she married an Irish king. A story I have heard (and am inclined to credit) is that she brought mystical Egyptian wisdom to blend with Druidical streams, in preparation for the coming of Christ, and that the Essene community in Judea from which the Blessed Mother Mary and Joseph came was of this lineage.
(And no this is not just an Irish-American's fanciful tale of how Jesus was really Irish! Though the Irish do tell a joke along these lines: "How do we know Jesus was Irish? Simple. At age 33 he had no job, lived at home, and his mother thought he was Jesus Christ!").
In any case, if we want to truly celebrate the Celtic Spirit on March 17th, I suggest we do so by honoring the two Marys - the Mother and the Magdalene - and the Universal Christ which was embodied in Yeshua ben Joseph. And by honoring the dazzling perseverance of the Irish, who have overcome centuries of oppression to reclaim their sovereignty, their language, and their strange irresistible charm!
"Go maire sibh bhur saol nua!"
(Irish Gaelic - "May you enjoy your new life!")