Angels and the created world
Catholic faith recognizes both the visible world and spiritual creatures called angels. Angels are created servants and messengers of God, not lesser gods or the souls of deceased people. The material world is also good: Christian hope does not require contempt for bodies or ordinary created things. Curiosity about spiritual beings should remain subordinate to trust in God and charity toward neighbors.
Follow the sources
An original library introduction, with sources for further study. This is a starting point rather than a complete treatment or a finished formation lesson.