Catechism of the Catholic Church §850 — excerpt
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."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: AG 2 · John Paul II, RMiss 23