Catechism of the Catholic Church §1578 — excerpt
No one has a right to receive the sacrament of Holy Orders. Indeed, no one claims this office for himself; he is called to it by God.
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.