What does the shamrock signify on the day of Saint Patrick's Day?

Answer 1

St. Patrick was a missionary to Ireland in the 5th century. He was attempting to convert the Celts away from paganism. A basic principle of paganism is that there are may gods or spirits. St. Patrick tried to explain that all of the gods that the pagans were worshiping were actually just the "One True God" in "Holy Trinity."

He used the 3-leafed clover or shamrock to illustrate the Trinity.

Interestingly, St. Patrick was using a similar argument that Apostle Paul used in Athens, where Greek polytheists had erected an alter to the "unknown god."

The popularization of the lucky 4-leafed clover is a rather modern myth. Since 3-leafed clover is common, a 4-leafed sprig is rare and considered lucky but is not generally associated with St. Patrick's Day or Ireland specifically.