Messenger bot (edit: BOY, goddammit!) didn't open the letter bc he knew he wasn't going to be able to read it and also he has no authority to go around opening the messages he carries. You on the other hand are an arrogant bastard, so you boldly open it. You show the lad the Onion, he knows what an onion is, and you tell him it's a symbol for all the layers of corruption in the aristocracy, which he's also seen that firsthand. You tell him there will be a new kind of messages, not for individual lords but for all the lowly people, which will peel away the layers and expose the corrupt to the ridicule of the masses, bringing laughter and ideas of revolution into their lives.