Safe delivery of messages
Since time immemorial, methods to transfer secrets between one another have existed, and were an important part of human history. People would whisper secrets in dark alleyways or sometimes even devise a code to prevent any potential eavesdroppers from understanding what they were saying.
However, these methods would only work if the speaker and listener were in close proximity. Without the advanced internet technology that lets us easily communicate long-distance, people in the past had to put their messages into envelopes and deliver them by conventional means. Only, there was one problem: the envelope could be intercepted during delivery and resealed once read, unbeknownst to the actual intended recipient. Even when messages were altered or falsified, the recipient had no way of knowing. You can imagine how difficult it must have been for a message to be sent and received safe and sound.
So there was a need for a new method of security. While it may have been impossible to prevent someone from reading the message, people thought of a way to mark the message with a seal that would let the recipient know who wrote the message and if someone had opened the envelope while it was being delivered. This was how sealing became a regular practice. Once the message was inside the envelope, the writer would pour melted wax onto the flaps and push down on the heated wax with a seal engraved with a unique pattern. Anyone attempting to read the message would have had to damage the seal, and the actual recipient would know if the message was compromised by checking if the seal was intact. Unique patterns were engraved onto these seals to prevent anyone from trying to apply a seal of their own after damaging the original. Sometimes, messages were hidden so that they would only be revealed by using a special ink.