Maewyn Succat, the the British son of a pagan Roman official named Calphurnius and the grandson of a Christian priest, was kidnapped at the age of sixteen by Irish pirates, and made a slave. His captivity seems to have been rather gentle; he was employed as a shepherd.by a Druid priest, Milchu, who treated him well. During his long days watching the flock, he meditated on the Christianity that seems not to have been especially important to him in earlier years.
He finally managed to escape. Once back in Britain, he had a vision in which an angel disclosed to him the Vox Hibernicus- the Voice of the Irish- calling him "noble youth" ("noble" in Gaelic is "padraig") to return to the land of his captivity and convert his former captors to Christianity. He changed his name from Maewyn ("Warlike") to the adjective the Vox Hibernicus had applied to him- Padraig- and was ordained a priest, consecrated a bishop, and given the official blessing of the Church to carry the Gospel to Ireland. His first act upon arriving there was to visit his former master, Milchu, and buy his freedom.
So successful was Patrick that, to the former slave's horror and sorrow, his former master committed suicide, vowing not to become a "slave" of the man who had once been his own slave.
St. Patrick is said to have driven the snakes out of Ireland. In fact, natural historians tell us, there never were snakes in Ireland to begin with. Most scholars believe that the "snakes" are actually a metaphor for the influence of paganism.
The shamrock became associated with Patrick- and with Ireland- because, according to legend, he was explaining the Christian faith one day to an Irish pagan who told him that he could not understand how God could at the same time be three and yet only one. To illustrate the doctrine of the Trinity, Patrick supposedly bent over and plucked a piece of clover- a shamrock. Never mind that the incident probably never took place, and that the use of the shamrock as an illustration of the Trinity results in the heresy of partialism; that's the legend, and that's the symbolism behind it.
Now, here is the crucial point: while the shamrock is nothing more than common clover, it does have one necessary attribute. A shamrock, by definition, has three leaves- no more, and no less. The four-leaf clover often confused with the shamrock on St. Patrick's day is not, in fact, a shamrock at all. The entire symbolism of the shamrock is as a metaphor for the Holy Trinity. If the number of leaves is other than three, the entire symbolism of the shamrock as regards St. Patrick- and thus, Ireland- is lost!
Sadly, we're seeing more and more four leaf clovers on St. Patrick's day- even among the Irish themselves, who should know better. It was rather depressing when, a few years ago, I even saw a sign covered with four leaf clovers rather than shamrocks advertising Beamish Irish Stout.
Now, it's not just that using a four leaf clover destroys the entire significance of the symbol. In an important sense, it turns that symbolism on its head. Patrick, a Christian bishop, firmly believed that our lives and the events they contain are firmly under God's control. But the four leaf clover is a symbol of the denial of that idea- of the pagan concept of luck.
I have no idea which came first: the use of the four leaf clover as a symbol of luck, or the concept that the Irish- a people whose history has been marked by poverty and suffering to a degree that few nations on Earth have known- are somehow, of all things, lucky. But it does seem, somehow, to be tied together with the confusion of a Christian symbol- the shamrock- with a pagan symbol, the four leaf clover. In themselves, he two may be nothing more than variations in the form taken by the same plant. But in terms of symbolism, they have less than nothing in common.
But in any case, if the metaphorical understanding of St. Patrick having driven the snakes from Ireland is valid,the snakes seem to have returned.