The basis for the Catholic Church has always been missionary work. Saints like Paul and Patrick are the people who made the Church strong.
Pope John Paul II has always been a great proponent for missionary works. "St. John tells us that 'God is Love' (1 Jn 4:8, 16). Every person therefore is invited to 'repent' and 'believe' in God's merciful love." In this quote, the Pope tells us that all people of all lands, races, and creeds are called to repent for their transgressions against God and to come to believe that God loves them unconditionally. This is the driving force behind missionary work; to bring others to God's love and unending mercy.
Both Saint Patrick and Saint Paul lived out their lives after their respective conversions as models of missionary life. These two Saints each went to groups that were considered barbaric by the Christians of their times.
Paul went to the Gentiles, or non-Jews. Patrick went to the Irish. In Paul's time, gentiles were looked down upon by all Jews. They were pagans and practiced traditions that sometimes included human sacrifice.