Catechism of the Catholic Church §2780 — excerpt
We can invoke God as "Father" because he is revealed to us by his Son become man and because his Spirit makes him known to us.
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.