The spear and jug served to affirm David’s statement that Abner had failed in his duties. They were evidence that Saul’s life was in David’s hands and that Abner did not protect Saul as he was meant to. Symbolically, with the king’s spear in the hand of David, Saul’s power was also shown to be gone. He had been disarmed by David and nothing could keep David from the kingdom.1
16 This thing that you have done is not good. As the LORD lives, you deserve to die, because you have not kept watch over your lord, the LORD’s anointed. And now see where the king’s spear is and the jar of water that was at his head.”