St. Patrick, whose feast day is celebrated by the Catholic Church on March 17, is credited with spreading Christianity throughout Ireland. Kidnapped and sold into slavery as a young man, St. Patrick became a devout Christian during his years in captivity. Guided by visions to return to Ireland as a missoinary, St. Patrick spent his life ministering to Christians already living in Ireland and converting the Irish.

Spreading Christianity Throughout Ireland St. Patrick used traditional Irish culture to describe the tenets of Christianity to its inhabitants. It was his idea to place a sun–a common symbol in Ireland– onto the Christian cross, so it would seem more natural to the Irish. This became what is known as the Celtic cross. St. Patrick is credited with explaining the mystery of the Holy Trinity to the people of Ireland by using a shamrock. It symbolized the Father, Son, and Holy Spirit, each leaf being separate but also part of the same plant. St. Patrick used this to teach about the concept of three persons in one being.