Originating from Ireland, the feast commemorates the death date of the foremost patron saint of Ireland, Saint Patrick and the arrival of Christianity in Ireland as well as Irish heritage and culture. Furthermore, due to the Irish diaspora, Saint Patrick's Day is being celebrated across the world, with the same colors, symbolism, customs, and beliefs being observed.
Green, white, and orange make up the national colors of Ireland, the lush landscapes are tinted in all shades of viridian, white clouds against a golden-hour tangerine sky. But during Saint Patrick's Day, everything goes as green as one of the festival's icons, the shamrock. According to the legend, Saint Patrick used the shamrock to explain the Holy Trinity to Irish pagans. Prior to Christianity, pagan Ireland had many triple deities, and the number "3" was considered an important digit, and thus, the three-leafed clover may have helped Saint Patrick himself to evangelize them.
There's also an Irish custom called "drowning the shamrock", in which the shamrock is placed in a cup, then filled with alcohol — traditionally whiskey, beer, or cider. It is meant to drink as a toast to Saint Patrick, Ireland, and fellow Irish. The three leaves are supposed to symbolize faith, hope, and love, making the shamrock a national symbol of Ireland.
If by chance, a four-leafed clover appears, the fourth leaf is said to be for good luck. Sometimes, people who celebrate Saint Patrick's Day would toss the drowned shamrock and toss it over for good luck. Faith, hope, love, and good luck? No wonder everyone's so keen to wear green!