In this chapter, David defeats the Ammonites and Arameans.
This is largely a continuation of the previous chapter, describing more of David's wars. The material for this chapter is mostly copied from 2 Samuel 10 with very little modification. The overall theme and purpose of this chapter is the same as the previous chapter: it is establishing the context for Solomon's construction of the temple by destroying Israel's national enemies and gathering in the wealth of the nations.
This chapter contains two separate stories. The first story is when the servants of David travel to Nahash's funeral, which is in verses 1-7. The second story is the battle between Israel and Ammon (plus their allies), which is in verses 8-19. I would like to share a lesson, or at least something interesting, from each story.
In the first story, it seems like the key tension is between David, who expresses support for Nahash, and Hanun who is distrustful of David. There's a couple different things we can learn from this story. First, we can see the troubled history between these two kingdoms. We know that Israel and Ammon fought many times (for instance, Judges 10:7-9), so it is natural that they would be hostile towards each other and we see that in Hanun's response to David. In this case, Ammon would be particularly distrustful because Israel has recently engaged in a series of wars against their neighbors, which we read about in the previous chapter. It seems only natural that Ammon would expect Israel to encroach upon them next.
David and Hanun signify their respective kingdoms, so I think what we see in Hanun's response is generations of malevolence being expressed. What's surprising to me is that David would look upon Nahash so favorably. We know from 1 Samuel 11 that Nahash king of Ammon attacked the Israelites in Gilead, and chronologically that is the most recent time we hear about Nahash before this story*, so we don't have any reason to think that David and Nahash have an alliance besides what we read in this chapter. One thing worth mentioning is that the phrase "I will show kindness to Hanun" in verse 2 has an implication that the two nations had an alliance of some sort. In fact, the International Standard Version (ISV) translates that phrase as "I will be loyal to Hanun". If they did have an alliance, it is a surprise to me because of the aforementioned hostility between these nations, but it does make Hanun's response to David's delegation much more disrespectful.
Second, I think this story shows the importance of spies and deception in ancient warfare. We should remember that Israel sent twelve spies into the promised land before they invaded (Numbers 13); Joshua also sent two spies into Jericho before they invaded that city (Joshua 2). Besides spying out the land, spies frequently served to find, bribe or threaten people into betraying their city and e.g. open the city gates during a siege or provide some other assistance to the attackers. This chapter itself shows us how much of a serious threat this could be. Even though Hanun did not kill the men, he probably stopped them from entering the city or gleaning much information.
Third, this story shows that while David sent his men in friendship, he became the enemy that Hanun feared because of how Hanun responded to him and treated him. I think it's ironic that Hanun's response created the very enemy that he feared, and resulted in the devastation of his kingdom. If he had treated David as a friend, he may have kept David as a friend. I think this is a good lesson for us because I think it's true in general that a lot of people will act similarly to what we expect from them. If you expect people to be honest and trustworthy, a lot of people step up to those expectations. Not everyone, but a lot of people. If you persistently expect people to be stupid or lazy or mean, many people step down to meet those expectations too, because you encourage what you expect from others. That doesn't mean we should expect everyone to be kind of honest because some people are rotten enough that they will take advantage of you, but I think the majority of people want to be good and kind and honest, and if you create an environment where they are treated like it, they will gradually become that kind of person (if they aren't already). In this chapter we see the converse, where David is treated like an enemy, so he becomes one.
In the second story, the main part I want to focus on is the two commanders who are helping each other, Joab and Abishai. I think this is a cool story because we see two men fighting two separate battles, but they make a promise to each other that if one of them starts to lose, the other will go and help him, and vice versa. Even though they were outnumbered and surrounded, they helped each other and were able to achieve victory. In the same way, we can strengthen each other even while we are fighting separate battles and together achieve victories that would not be possible alone. It was after the victory of Joab that the enemies of Abishai fled before him (v. 15).
In the next chapter, the wars conclude with some final battles against the Ammonites and the Philistines.
*We read in 2 Samuel 17 that Shobi son of Nahash brings food and drink to David when he is exiled by his son Absalom, but that is chronologically after the events described in this chapter. This suggests that there is still some spark of affection between the Ammonites and David, though perhaps they only supported David because they saw him as an insurgent hostile to the current king Absalom at the time, and wanted to encourage division and warfare in Israel. But that's neither here nor there.