Therefore hear, ye {q} nations, and know, O congregation, what is among them.

(q) God takes all the world to witness and the insensible creatures of the ingratitude of the Jews.

Wesley's Notes

6:18 Nations - He calls upon the nations round about to be spectators of his severity against Judah. What - The greatness of their punishment, as the effect of the greatness of their sins.

Jamieson-Fausset-Brown Bible Commentary

18. congregation-parallel to "nations"; it therefore means the gathered peoples who are invited to be witnesses as to how great is the perversity of the Israelites (Jer 6:16, 17), and that they deserve the severe punishment about to be inflicted on them (Jer 6:19).

what is among them-what deeds are committed by the Israelites (Jer 6:16, 17) [Maurer]. Or, "what punishments are about to be inflicted on them" [Calvin].

Matthew Henry's Concise Commentary

6:18-30 God rejects their outward services, as worthless to atone for their sins. Sacrifice and incense were to direct them to a Mediator; but when offered to purchase a license to go on in sin, they provoke God. The sins of God's professing people make them an easy prey to their enemies. They dare not show themselves. Saints may rejoice in hope of God's mercies, though they see them only in the promise: sinners must mourn for fear of God's judgments, though they see them only in the threatenings. They are the worst of revolters, and are all corrupters. Sinners soon become tempters. They are compared to ore supposed to have good metal in it, but which proves all dross. Nothing will prevail to part between them and their sins. Reprobate silver shall they be called, useless and worthless. When warnings, corrections, rebukes, and all means of grace, leave men unrenewed, they will be left, as rejected of God, to everlasting misery. Let us pray, then, that we may be refined by the Lord, as silver is refined.