1 Samuel 25 seems to be very important

I think this has struck me before. Re-reading 1 Samuel, we find that:

• Saul is rebuked by Samuel (1 Samuel 15)
  • David has to flee to the Philistines (1 Samuel 21)
    • The Ziphites betray David to Saul, then David spares Saul's life (1 Samuel 23-24)
      • Samuel dies (1 Samuel 25:1)
      • David accepts Abigail's gift, and marries her after God kills her fool of a husband (1 Samuel 25:2ff)
    • The Ziphites betray David to Saul, then David spares Saul's life (1 Samuel 26)
  • David lives among the Philistine (1 Samuel 27)
• Saul is rebuked by Samuel (1 Samuel 28)

Now: I know …: Chiasms are a little like white elephants, and if you're not careful you start to see them everywhere.

But, it does seem that chapter 25 is a key chapter, making those two events (the death of Samuel, and the death of Nabal) key events in the episode that is David's flight from Saul. They may offer a clue as to the purpose of the lengthy record we have of that period of David's life. The question is: What clue? Comments please!