Catechism of the Catholic Church §425 — excerpt
The transmission of the Christian faith consists primarily in proclaiming Jesus Christ in order to lead others to faith in him. From the beginning, the first disciples burned with the desire to proclaim Christ: "We cannot but speak of what we have seen and heard."
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.