St. Patrick's Day 

1) St. Patrick was a man who made extensive missionary work in Ireland which is mostly why he's famous . During thirty years, he supposedly converted 135,00 people, established 300 churches,and consecrated 350 bishops. He was enslaved in Ireland and learned their rituals and custom and language and it was these people that he had converted into Catholicism. He managed to escape but the people begged him to come back so he established catholic teachings in Ireland and managed to convert some of the Celtic symbolism and Christianize them. He used the clover as a sign of trinity. 

2) The purpose was to celebrate the Roman Catholic feast of the patron saint of Ireland and the arrival of Christianity to Ireland. It celebrates the heritage and culture of Irish in general . 

3) It is celebrated in March 17 Because it is the traditional day that Saint Patrick died. 

4)We wear green because it represents the return of spring as well as the Irish culture.