Catechism of the Catholic Church
329 St. Augustine says: "'Angel' is the name of their office, not of their nature. If you seek the name of their nature, it is 'spirit'; if you seek the name of their office, it is 'angel': from what they are, 'spirit', from what they do, 'angel.'" 188 With their whole beings the angels are servants and messengers of God. Because they "always behold the face of my Father who is in heaven" they are the "mighty ones who do his word, hearkening to the voice of his word". 189
330 As purely spiritual creatures angels have intelligence and will: they are personal and immortal creatures, surpassing in perfection all visible creatures, as the splendour of their glory bears witness. 190
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.