Catechism of the Catholic Church §876 — excerpt
Intrinsically linked to the sacramental nature of ecclesial ministry is its character as service. Entirely dependent on Christ who gives mission and authority, ministers are truly "slaves of Christ," in the image of him who freely took "the form of a slave" for 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.