Charles Ellicott Commentary Jeremiah 49:20

"Therefore hear ye the counsel of Jehovah, that he hath taken against Edom; and his purposes, that he hath purposed against the inhabitants of Teman: Surely they shall drag them away, [even] the little ones of the flock; surely he shall make their habitation desolate over them." — Jeremiah 49:20 (ASV)

Surely. —Literally, If not ... —the strongest Hebrew idiom of solemn declaration.

The least of the flock shall draw them out ... —The English is obscure, probably because the object of the verb has been taken as its subject. Better, Surely they (i.e., the Chaldean invaders) will vex them, the feeble ones of the flock; surely he will make their pasture terror-stricken at them. The thought expressed is that the very fields of Edom would, as it were, shudder at the cruelty of their conquerors. It is noticeable that the whole passage is repeated in Jeremiah 50:44-45, and is there applied to Babylon.