Catechism of the Catholic Church §729 — excerpt
Only when the hour has arrived for his glorification does Jesus promise the coming of the Holy Spirit, since his Death and Resurrection will fulfill the promise made to the fathers.
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.