Catechism of the Catholic Church §852 — excerpt
Missionary paths. the Holy Spirit is the protagonist, "the principal agent of the whole of the Church's mission." It is he who leads the Church on her missionary paths.
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: John Paul II, RMiss 21 · AG 5 · Tertullian, Apol. 50, 13: PL 1, 603