Catechism of the Catholic Church §1076 — excerpt
The Church was made manifest to the world on the day of Pentecost by the outpouring of the Holy Spirit. The gift of the Spirit ushers in a new era in the "dispensation of the mystery" the age of the Church, during which Christ manifests, makes present, and communicates his work of salvation
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: SC 6 · LG 2