We find ourselves with David on the run and Absalom trying to figure out how best to defeat David. Keep in mind this is a son going after his father. His primary counsel told the now king to pursue David right away and to take David out and then the remaining troops would come home with their tail between their legs and swear allegiance to Absalom. He likes that advice, but asked another counselor for a second opinion. He gave different advice. He said to gather all of Israel and that Absalom should be the one to pursue him and then publicly kill David so that forever the people would be tied to him. Absalom actually like that even better.
The one who had given the first advice and who was used to being listened to, packed up his belongings, got on a donkey, went home, and killed himself. He no longer felt needed. The one who gave the new king advice was actually on David's side and so David was warned of what was going to happen next.
You can palpably feel a build up of what is going to take place and you have to know that it doesn't bode well for Absalom. If you didn't know that then all you would need to do is look at vs.14 where we read that:" the Lord had ordained to defeat the good counsel of Ahithophel, so that the Lord might bring ruin on Absalom." You have a sense that ruin is about to fall on Absalom as he pursues his father to grab all the power he could.