Saint Patrick was said to have used the shamrock to explain to the Irish people the doctrine of the Trinity. He spent thirty more years in Ireland and died on the 17th of March, 461. He is considered the principal missionary from Rome to the Irish and is celebrated as such on this day.
Today Saint Patricks day is celebrated around the world as a sort of tribute to the Irish and the culture of Ireland, a relatively small Island with a storied past and perhaps more storied characters within. It is, of course, widely known for its association with the drinking of beer. Saint Patricks day is the day in which the most alcohol is consumed by Americans. You can just see Saint Patrick now, can’t you, wandering into an American bar well after midnight, laying down on the floor next to a passed out college student, pointing at the paper shamrocks stapled to the ceiling, and explaining how much the Father loves the Son, and the Son loves the Father, and how the Holy Ghost is with us always, even on the floor of a pub.