St. Patrick, the patron saint of Ireland, used the three-leafed shamrock to explain the Trinity. He used it in his sermons to represent how the Father, the Son, and the Holy Spirit could all exist as separate elements of the same entity.

Saint Patrick’s Day (Irish: Lá ’le Pádraig or Lá Fhéile Pádraig), colloquially St. Paddy’s Day or Paddy’s Day, is an annual feast day which celebrates Saint Patrick (circa 385–461 AD), one of the patron saints of Ireland, and is generally celebrated on March 17.

The day is the national holiday of Ireland. It is a bank holiday in Northern Ireland and a public holiday in the Republic of Ireland, Montserrat, and the Canadian province of Newfoundland and Labrador. In the rest of Canada, the United Kingdom, Australia, the United States and New Zealand, it is widely celebrated but is not an official holiday.