I started reading a couple of books on Irish and Celtic history and spirituality because my wife and I went to Ireland as a sort of late anniversary present. I have been surprised to find out what Western Civilization owes to the Irish. When all of Europe was plunging into the Dark Ages, the Irish Christians were preserving much of the Greek and Latin Literature that we have today, including the Gospels -- one of the more famous Gospel manuscripts being the beautiful Book of Kells.
In addition to preserving literature they brought needed change (shall we dare say reform?) to Christianity. By the 5th century Christianity had become a Roman religion. To be Roman meant being a Christian, and being Christian mean being Roman, christians of this era didn't ever think of preaching the Gospel to Barbarians (those outside the Roman empire). The rigidity and hierarchy of 5th century Roman Catholicism could not be translated into the Irish tribal culture. However, a Roman named Patricius, who was once a slave in Ireland, would return to Ireland after being told to by God in a dream and find that the Irish were a spiritual people quite ready to receive the Gospel. They saw the divine in creation as Paul did, but this was quickly lost in Romanized Christianity. In short they believed God to be both Transcendent and Immanent.
This sense of the world as holy, as the Book of God - as a healing mystery, fraught with divine messages - could never have risen out of Greco-Roman civilization, threaded with the profound pessimism of the ancients and their Platonic suspicion of the body as unholy and the world as devoid of meaning. Even Augustine, whose synthesis of pagan and Christian attitudes is the most remarkable philosophical creation of Christianity's first five centuries, can come nowhere near Patrick's originality. True, Augustine's theories on sin will haunt the Middle Ages, and cast their shadow still. But from the celebratory spirit of the 'Breastplate' will spring the characteristic art and poetry of the western world.
--Thomas Cahill, How the Irish Saved Civilization
I'm sure this doesn't begin to scratch the surface of their contribution to western civilization and christianity -- I have come to appreciate their influence, which can still be heard in 20th century Irish poets:
I see his blood upon the rose
And in the stars the glory of his eyes,
His body gleams amid eternal snows,
His tears fall from the skies.
I see his face in every flower;
The thunder and singing of the birds
Are but his voice - and carven by his power
Rocks are his written words.
All pathways by his feet are worn,
His strong heart stirs the ever-beating sea,
His crown of thorns is twined with every thorn,
His cross is every tree.
-- Joseph Plunkett