John Gill Commentary Jeremiah 49:8

"Flee ye, turn back, dwell in the depths, O inhabitants of Dedan; for I will bring the calamity of Esau upon him, the time that I shall visit him." — Jeremiah 49:8 (ASV)

Flee ye, turn back, dwell deep, O inhabitants of Dedan
Another city in Idumea; though some take it to be a country in Arabia, bordering on Edom, and subdued by the Edomites: the inhabitants of this place are advised to "flee" for their lives, since the enemy was just upon them; and "turn back", lest they should fall into his hands; and hide themselves in some deep caverns of the earth, in holes, and dens of rocks, and such like places. It is a prophecy that they should flee from and turn their backs on their enemies, and betake themselves to some very secret places for safety;

for I will bring the calamity of Esau upon him ;
which was determined concerning him, threatened to him, and was his just desert; even the utter destruction of the whole land:

the time of his visitation ;
the time fixed to visit him in a way of wrath and punishment being come,