Charles Ellicott Commentary Jeremiah 49:3

"Wail, O Heshbon, for Ai is laid waste; cry, ye daughters of Rabbah, gird you with sackcloth: lament, and run to and fro among the fences; for Malcam shall go into captivity, his priests and his princes together." — Jeremiah 49:3 (ASV)

Howl, O Heshbon, for Ai is spoiled. —Heshbon has appeared in Jeremiah 48:2; Jeremiah 48:45, as connected with the fortunes of Moab, but it was strictly an Ammonite city. The “Ai” here is obviously not the city near Jericho of Joshua 8:28, and unless we assume an error in the text (“Ai” for “Ar” = city), we must infer the existence of a Trans-jordanic city of the same name.

Run to and fro by the hedges. —Hedges, in the English sense of the word, have never been common in the East, and the word here denotes either the palings round the sheepfolds, or the walls round the vineyards of the villages that are described as the “daughters of Rabbah.” The word is never used for the walls of a city, but appears in Numbers 22:24; Numbers 32:16; Numbers 32:24; Numbers 32:36 in the sense of “sheepfolds.”

Their king shall go into captivity. —Better, as before, Melcom. As in Jeremiah 48:7, the captivity of the national deity with his priests (the fact that they are named is decisive as to the meaning) involves the captivity of the people.