A true prophet often has to deliver difficult news that shatters the hopes of regional powers. In this instance, the message is a harsh reality: submission to the Babylonian empire is a decree that applies to everyone without exception. Jeremiah directs this firm warning straight to the foreign envoys who have traveled to Jerusalem [רש"י].
There is a specific reason the prophet shares with these foreign ambassadors the exact same warning he previously delivered to Zedekiah, the king of Judah. The message serves as a sharp political wake-up call. He wants the envoys to understand that forming a military alliance with Judah will be completely useless. Zedekiah cannot offer them any protection, as he is under the exact same absolute obligation to surrender to the Babylonian king [מלבי"ם].
The practical instruction given to these nations is clear and direct. They must willingly accept Babylonian rule and place themselves under its authority. Only by choosing this path of surrender can they guarantee their own survival and avoid utter destruction [מצודת דוד, ביאור שטיינזלץ].