What does 2 Samuel 17:4 mean?

Ahithophel is wise in the ways of the world (2 Samuel 16:23). First, he told Absalom to have sex with David's concubines, This would reassure the people that Absalom would not betray his followers by trying to make amends with David. The gesture shows Absalom is severed from David and dedicated to being king (2 Samuel 16:20–22). Now, Ahithophel has offered to take immediately available men to hunt David before the king can catch his breath. They'll kill David and bring back his people, like friends of the bridegroom rescuing a kidnapped bride (2 Samuel 17:1–3). Absalom and the elders believe Ahithophel's plan will work.

Neither Absalom nor Ahithophel know that God allowed them to rebel against David and take Jerusalem for an extremely specific purpose. As David took Uriah's wife and had him murdered, so God promised that another would sleep with David's wives and betray him (2 Samuel 12:9–12). Now that they have fulfilled God's curse on David, they need to pay for their sin against him.

David set that stage by convincing his old friend Hushai to infiltrate Absalom's court and counter Ahithophel's advice (2 Samuel 15:32–37; 16:16–19). When Absalom asks Hushai what he thinks of Ahithophel's plan, Hushai will be ready. He will tell Absalom it's no good. He will suggest that David and his men aren't going to scatter in the face of an army. They're too experienced—and far too angry. As soon as Ahithophel's army sees blood, they'll lose all courage (2 Samuel 17:5–10).

Instead, Hushai will suggest Absalom call on men from throughout the twelve tribes. Then a massive army can join under their new king to overwhelm David and his fighting men (2 Samuel 17:11–13). This suggestion plays on Absalom's vanity, fear, and inexperience. Absalom falls for Hushai's secret sabotage, a mistake that gives David time. Hushai goes to the priests and gives them a message for their sons. David receives the warning: to cross the Jordan with his people and get to safety (2 Samuel 17:14–22).