Why the Shamrock

St. Patrick was a Christian missionary that came to Ireland to teach about God. He found that the Irish had great difficulty comprehending the doctrine of the Trinity, St. Patrick held up a shamrock (similar to a three-leaf clover) to show how the three leaves combined to make a single plant, just as the Father, Son, and Holy Ghost combined to make the Holy Trinity.  The Irish understood at once, and from that time the shamrock has been the symbol of the land.  Irishmen wear it in their hats on the saint's day.