Albert Barnes Commentary Jeremiah 46:4

"Harness the horses, and get up, ye horsemen, and stand forth with your helmets; furbish the spears, put on the coats of mail." — Jeremiah 46:4 (ASV)

From the infantry, the prophet proceeds to the chariots, in which the Egyptians placed great confidence.

Get up, ye horsemen — Or, “mount the steeds.”

Furbish — that is, polish, sharpen.

Brigandines — In old times, a brigand meant a soldier, and we still call a division of an army a brigade, and a commander a brigadier, that is, a brigandier, or captain of brigands. Similarly, a brigandine means a soldier’s equipment and is used here for a coat of mail.