Mission - a requirement of the Church's catholicity
The origin and purpose of mission. The Lord's missionary mandate is ultimately grounded in the eternal love of the Most Holy Trinity: "The Church on earth is by her nature missionary since, according to the plan of the Father, she has as her origin the mission of the Son and the Holy Spirit." The ultimate purpose of mission is none other than to make men share in the communion between the Father and the Son in their Spirit of love.
Source: Catechism of the Catholic Church (Vatican.va)