What does Jeremiah 37:7 mean?

This is what the Lord, Israel's God, says: Tell the king of Judah who sent you to ask me, 'The Egyptian army that came to help you is going to turn around and head back to Egypt.' Jeremiah 37:7 - Modern Text Bible

(God tells Jeremiah to deliver a message to King Zedekiah: the Egyptian forces Judah hoped would save them are leaving, so their help won't last.)