The Spirits' Book
Book Two - The Spirit World
Chapter IX - Intervention of Spirits on the Physical World
Guardian Angels: Protective, Familiar and Sympathetic Spirits
493. Is the mission of a protective spirit voluntary or obligatory?
“Your protective spirit is duty-bound to watch over you, having accepted that task. Spirits can choose their wards from a selection of like-minded beings. In some cases, this position is a pleasure, while in others it is a job or duty.”