325 The Apostles’ Creed professes that God is “creator of heaven and earth”. The Nicene Creed makes it explicit that this profession includes “all that is, seen and unseen”.
326 The Scriptural expression “heaven and earth” means all that exists, creation in its entirety. It also indicates the bond, deep within creation, that both unites heaven and earth and distinguishes the one from the other: “the earth” is the world of men, while “heaven” or “the heavens” can designate both the firmament and God’s own “place” — “our Father in heaven” and consequently the “heaven” too which is eschatological glory. Finally, “heaven” refers to the saints and the “place” of the spiritual creatures, the angels, who surround God.
327 The profession of faith of the Fourth Lateran Council (1215) affirms that God “from the beginning of time made at once (simul) out of nothing both orders of creatures, the spiritual and the corporeal, that is, the angelic and the earthly, and then (deinde) the human creature, who as it were shares in both orders, being composed of spirit and body.”
The existence of angels — a truth of faith
328 The existence of the spiritual, non-corporeal beings that Sacred Scripture usually calls “angels” is a truth of faith. The witness of Scripture is as clear as the unanimity of Tradition.
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.’” 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”.
330 As purely spiritual creatures angels have intelligence and will: they are personal and immortal creatures, surpassing in perfection all visible creatures, as the splendor of their glory bears witness.
Source: Catholic Catechism