Hi, Shelby —

Because it is used to seal documents.

In ancient days, instead of a signature, people would use a ring with a unique relief on it like a coat of arms. They would create an envelope and pour molten wax to seal it, then impress the ring into the warm wax to form an image.

This proved who authorized the document. If the ring wasn't destroyed, documents could be forged in the name of the pope.

Eric