Catechism of the Catholic Church §767 — excerpt
"When the work which the Father gave the Son to do on earth was accomplished, the Holy Spirit was sent on the day of Pentecost in order that he might continually sanctify the Church."
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.
Whole chapters cited: Matthew 5 · Matthew 6
Also cites: LG 4 · AG 4 · AG 2