In this chapter, David becomes king and conquers Jerusalem.
As my readers have probably already noticed, this chapter has a lot in common with Samuel, particularly 2 Samuel 5, just as the previous chapter was largely copied out of 1 Samuel 31. There's a few things I want to say about this before we move on.
Many of my readers may be getting bored of Chronicles at this point wondering, why so much repetition? I read this story already! Why can't they get to something new or different? To try and answer those questions, do you folks remember way back in Genesis 24 when the narrative repeated the servant's story twice? And do you remember later in Exodus when chapters 25-31 were largely (but not entirely) copied in Exodus 36-39? At the time, when explaining those chapters, I said that the repetition was probably a literary device that simply held over from the oral tradition that underlies much of the Pentateuch. However, Chronicles is very different because Chronicles is a completely separate book from Samuel (while the repetition in the Pentateuch is in the same book) and Chronicles does not have an underlying oral tradition, since as it should be clear from 1 Chronicles 9:1, Chronicles is mostly copied from a previous book. Even though both of these are instances of copying prior stories, they serve fundamentally different purposes which we can discern through the context.
In a nutshell, Genesis and Exodus contain repetition to help speakers memorize the passages, but Samuel and Chronicles contain repetition because the author of Chronicles wanted to make a point. We can find that point by studying the omissions and additions that made it into Chronicles, and that will be the main focus of my commentary for the remainder of this book.
In this chapter, the biggest difference from the Samuel narrative is that the Chronicler left out 2 Samuel chapters 1-4. That includes David's retribution against Saul's murderers and (perhaps more significantly) the civil war that followed between David and Ish-Bosheth. It also avoids the seven years in which David reigned over Judah from Hebron and jumps almost immediately to his unified kingship from Jerusalem. Because of the copying from 2 Samuel 5:1, it tells us that David was at Hebron, but Chronicles never explains why he is at Hebron. The main purpose of this narrative gap is to skip over the disunity and resistance to David's kingship, and present David as if he immediately became king with backing from all the people.
This chapter serves two basic purposes. First, it establishes David's authority over, and unified support from, all the tribes of Israel. It does this both in verses 1-3 when the people of Israel come to make David king, and it does this also in verses 10-47 which list David's champions. Importantly, many of those champions come from tribes besides Judah including Benjamin. Benjamin is particularly relevant because it is Saul's tribe (David's adversary) and because Benjamin was one of the major tribes returning from the exile (as discussed in chapter 9). The author of Chronicles is trying to minimize the former antagonism between Judah and Benjamin by presenting David as the king of the whole nation and presenting him as having the support of all the tribes, including Benjamin. I think this is a big deal to the Chronicler because this entire section (verses 11-47) are copied from 2 Samuel 23, which in the book of Samuel is not even part of the main narrative, it is in the appendix along with "miscellaneous stories", as I think they may be called. Here, the Chronicler has placed this list of men right at the very beginning of David's reign but with a very important preamble in verse 10 that you do not find in the Samuel narrative. Verse 10 explains the purpose of verses 11-47: it is to establish the list of very mighty men who supported David to make him king, together with all Israel. Therefore the Chronicler sees this as a natural extension of verses 1-3 when the elders and the people came to make David king.
The second purpose of this chapter is to establish Jerusalem, freshly conquered from the Jebusites, as the future site for the temple to the LORD. Chronicles spends a considerable amount of space discussing the preparations and construction of the temple. It is clear (for various reasons) that the Chronicler is deeply interested in the temple, and the conquest of Jerusalem forms the background for that later temple narrative. From that perspective, these few verses (4-9) are a small but indispensable part of the larger narrative.
If my readers are interested in more information on the names of the people mentioned in the list of heroes, see my commentary on 2 Samuel 23. Otherwise, I should mention that the lists of names between these two chapters are not exactly identical (1 Chronicles 11 contains several extra names compared to 2 Samuel), but the differences are not notable or well-understood.
The next chapter continues the theme of David's unified support from all the tribes.