Breadcrumb: Never murder a king

In 2 Samuel 4, for the second time in as many readings, we encounter a case of regicide. Two of Ishbosheth's captains, Rechab and Baanah, see which way the wind is blowing and decide to take matters into their own hands. They go into Ishbosheth's house during the king's midday nap on the pretence of fetching wheat, and then they stab the king through the belly. The decapitate the corpse and bring the severed head to David, thinking that they'll get what's coming to them for killing his biggest rival. And they do get what's coming to them, though not in the way they thought, because David has them both killed for regicide. And here we see how well David plays his cards: he's making it absolutely, unequivocally clear that you don't kill kings, even if they happen to be your enemies. We can only assume that the message stuck when he himself was king, because he reigned for a full 33 years before he died.