2 Samuel 15:14

Let us flee. The decision was wise, for David at the moment was totally unprepared for the crisis. In his great peril David shook off his lethargy and indecision and seemed to regain something of his early courage and swiftness of action. The sequel proved this to have been the correct course of action. Both Ahithophel (2 Samuel 17:1, 2) and Hushai (2 Samuel 17:7-13) recognized that delay would be fatal, and that Absalom’s greatest hope for success would be to take immediate steps against David. By his flight David gave himself time to make ready a defense, and the people time to ponder their course. The horrors of a long civil war were thus averted.

Smite the city. David feared that he could not at the moment make a successful stand at Jerusalem. Disaffection within the city, or perhaps even in his own household, might turn the tide against him. There would not be the spirit of unity that could have been expected if Jerusalem had been attacked by a foreign foe. It was his own son who would make the assault, and he undoubtedly had many supporters within the city.