Charles Ellicott Commentary Jeremiah 6:23

"They lay hold on bow and spear; they are cruel, and have no mercy; their voice roareth like the sea, and they ride upon horses, every one set in array, as a man to the battle, against thee, O daughter of Zion." — Jeremiah 6:23 (ASV)

Bow and spear. —As before (Jeremiah 5:16), the special weapons of the Chaldeans. The “spear” was a javelin, shot or hurled against the enemy.

Cruel. —The ferocity of the Chaldeans seems to have been exceptional. Prisoners impaled, or flayed alive, or burnt in the furnace (Jeremiah 29:22; Daniel 3:11), were among the common incidents of their wars and sieges.

They ride upon horses. —This appears to have been a novelty to the Israelites, accustomed to the war-chariots of Egypt and their own kings rather than to actual cavalry. (Job 39:21–25; Habakkuk 1:8; Isaiah 30:16.) Both archers and horsemen appear as prominent in the armies of Gog and Magog, i.e., of the Scythians, in Ezekiel 38:4; Ezekiel 39:3.

Set in array ... —The Hebrew is singular, and implies a new clause. It (the army of bowmen and riders) is set in array as a warrior, for war against you.