What does 1 Samuel 26:16 mean?

'You and your men deserve to die, because you didn’t guard your master, the Lord’s chosen one. Look around—where’s the king’s spear and water jug that were by his head?' 1 Samuel 26:16 - Modern Text Bible

(David proves his point by showing he has Saul’s spear and water jug, evidence that he was right next to Saul while everyone slept.)