What does 2 Samuel 15:27 mean?

The king said to Zadok the priest, 'Listen, go back to the city in peace, you and your son Ahimaaz, and Abiathar and his son Jonathan. I’ll wait at the river crossings in the wilderness until I hear from you.' 2 Samuel 15:27 - Modern Text Bible

(David sets up a way to get news from Jerusalem, using the priests and their sons as messengers.)