Albert Barnes Commentary Jeremiah 50:25

"Jehovah hath opened his armory, and hath brought forth the weapons of his indignation; for the Lord, Jehovah of hosts, hath a work [to do] in the land of the Chaldeans." — Jeremiah 50:25 (ASV)

By a grand figure, the prophet describes Yahweh arming Himself so that He personally may execute justice upon the wicked city.

For this is the work— Rather, for my Lord Yahweh of hosts has a work to do in the land of the Chaldeans.