A more thorough explanation:

Definition: A guardian of the spiritualities is a person who has the authority to exercise the spiritual and ecclesiastical jurisdiction of a diocese when the bishop is absent or there is a vacancy in the see.

For example, when a bishop retires or passes away, there is a period of time when the diocese is without a bishop. During this time, a guardian of the spiritualities may be appointed to oversee the spiritual and ecclesiastical matters of the diocese until a new bishop is appointed.

Another example would be if a bishop is unable to perform their duties due to illness or other reasons. In this case, a guardian of the spiritualities may be appointed to temporarily take on the responsibilities of the bishop.

These examples illustrate how a guardian of the spiritualities serves as a temporary leader and caretaker of a diocese's spiritual and ecclesiastical matters in the absence of a bishop.