Matthew Poole and continuators on Jeremiah 6:18

18 ¶ Therefore hear, ye nations, and know, oh congregation, what is among them.

He calls upon the nations round about to be, as so many spectators of his severity against Iudah, though they were his own people. 1. Partly to vindicate the justice of his proceedings, that they may not think him too severe. 2. Partly to shame them, if thereby he may bring them to repentance, and therefore he makes them witnesses as well of their sin, as of their punishment, ver. 10. Besides, 3. It is a secret upbraiding them, as if the Nations were more ready to understand, then they.

Either of Israel, and then the next words must be which are among them; or rather, of all nations, as supposing them gathered all together, Psal. 7.7. God is willing, that all the World should be witness of the equity of his proceedings.

Or that which is among them, the relative put for the Antecedent; either the height of their wickedness, or the severity of their judgments; understand it either way, or both wayes, and then it is the greatness of their punishment, as the effect of the greatness of their sins.