If you’re going to carry a message for someone, it makes sense that you want to know if the person who is charging you to deliver the message is trustworthy. You want to be assured that you’re delivering an honest and accurate message. Jeremiah spent over forty years declaring a message to the Israelite people, a message they did not want to hear or believe. It makes perfect sense, then, that God would give Jeremiah assurance the message he was to deliver was truthful. Moses wanted such a confirmation, and Jesus gives His disciples (including us) similar assurances.