"A curse on those who are lax in doing the LORD's work! A curse on those who keep their swords from bloodshed!" (NIV)
Cursed be he who does the work of the Lord negligently [with slackness, deceitfully]; and cursed be he who keeps back his sword from blood [in executing judgment pronounced by the Lord]. (AMP)
Cursed be he that doeth the work of the LORD deceitfully, and cursed be he that keepeth back his sword from blood. (KJV)