Chiasm: 2 Samuel 21-24

Here is a chiasm I found the few days ago from the end of 2 Samuel: 


A: God's Judgment and heed of supplications - famine (21:1-14)
    B: David's warriors kill Giants of Gath  (21:15-22)
        C:  Poetry - David's song of Deliverance (22:1-51)
        C': Poetry - David's oracle of last words (23:1-7)
    B': David's warriors and their renown (23:8-38)
A': God's Judgment and heed of supplications - pestilence (24:1-25)


Haven't yet figured out why the author chose to put these all in a chiasm. What further interpretation can we gain from observing this chiasm? 

Here is yet another look at the same passage: 

A David intervenes (21:1-14) Royal intervention – 21:14

   B Accomplishments in Battle (21:15-22) Royal warfare

     C David's praise (22:1-51) Royal words: 22:51

     C' David's Wisdom (23:1-7) Royal words: 23:5

   B' Accomplishments in Battle (23:8-39) Royal warfare

A' David intervenes (24:1-25) Royal intervention – 24:25