“Cursed be
The one
Who is slack
In doing
The work of Yahweh!
Cursed be
The one
Who keeps back
The sword
From bloodshed.”
Jeremiah seems to indicate here that you should not be slack in doing the work of Yahweh. Since the work of Yahweh here is killing the Moabites, holding back your sword from bringing bloodshed would mean that you would be cursed also.