As God’s king, David was obligated to uphold God’s law in Israel (Deuteronomy 17:18–20). In this case, the law required the death of Joab because he had murdered a fellow Israelite (Genesis 9:6; Exodus 21:12; Leviticus 24:17; Numbers 35:30–31). Since he was not at this point in time in a position to have Joab executed (see 2 Samuel 3:39; 1 Kings 2:5–6), David pronounced a curse upon him. The curse of David is a summary of the curses found for lawbreakers in Leviticus 26:14–39 and Deuteronomy 28:15–68.1 This curse is similar to Samuel’s prophecy regarding the house of Eli (1 Samuel 2:31–36).2
29 May it fall upon the head of Joab and upon all his father’s house, and may the house of Joab never be without one who has a discharge or who is leprous or who holds a spindle or who falls by the sword or who lacks bread!”