Insulted, his hesed greeted with contempt, David . . . does nothing. He sends the messengers to Jericho to wait for their hair to grow back (v. 5), but nothing more. There are no war preparations in Israel, no retribution. David does not return insult for insult, evil for evil. He has had long practice in bearing humiliations and being unjustly mistreated. It's the story of his life, at least during Saul's reign.
...
Meanwhile, David returns kindness for kindness, curbs his passion for revenge, lets things go, and ends up with another crown in his collection. Somebody is defending David's honor, and but it's not David.
Source: Peter Leithart - "David's Restraint, Yahweh's Trap", First Things Blog, 23 Jan 2017, https://www.firstthings.com/blogs/leithart/2017/01/davids-restraint-yahwehs-trap