In this chapter, the LORD punishes Israel for following other gods.
This chapter actually summarizes a lot of the things I said about Israel's failings in the last chapter and the themes of Judges in the introduction. Verses 11-19 are basically a rephrasal of what I call the Judges Cycle.
The best way to understand this chapter is to think of it as a continuation of the introduction that we read in the last chapter. In fact, I would surmise that this chapter and the previous were meant to be read at the same time, as part of the same message. The last chapter ended by listing all of the cities and towns that Israel did not capture, and this chapter begins by rebuking Israel for making covenants with the native Canaanites. So thematically, this chapter directly relates to what the previous chapter was talking about.
Secondly, just as in Judges 1, this chapter does not have a strict chronology. The beginning of the chapter (v. 1-10) is talking about events that happened before Joshua died, while verses 11-23 are actually describing the rise and fall of the Judges in general. The stories of these same Judges form the content of this book, so in essence this chapter is summarizing the stories we are about to read.
Briefly, this chapter is the author himself providing a theological commentary on the book we are about to read. He is summarizing the lives of the Judges and explaining why the events happened as they did, and he finds that the root cause is Israel forgetting the things the LORD has done (v. 10) and then doing evil and serving other gods (v. 11-12). Since I already wrote about the Judges Cycle at length I don't really want to repeat myself, but at this point I think it's fair to say that the author of Judges agrees with me (or more truthfully, I agree with him). :)
Now that I have stated the best way to read this chapter (as itself a commentary, not really part of the story), there are a few other things worth talking about in this chapter. I'll start at the beginning with verses 1-5. I have always found this story peculiar, for the following reason. When the angel of the LORD rebukes the people, v. 4 says that the people wept and v. 5 says that they offered sacrifices. What confuses me is, why didn't they just turn around and attack those nations that they did not destroy in chapter 1? With Gibeon I understand, because they made a covenant and cannot break their oath. Verses 21-23 says that the LORD left some of the nations as a test for Israel, to see if Israel would be faithful. But v. 2 seems to imply that Israel made peace with the Canaanites in the promised land, so unless that is only referring to Gibeon, it seems like there is more Israel can do than just cry, they should be attacking the Canaanites as they were commanded to do.
I guess what I'm trying to say is that Israel seems to be acting hypocritically, crying when they are rebuked but not correcting their behavior. Why should they cry if they don't repent (i.e. fix their behavior)? I've never really understood this story.
The rest of this chapter is just a summary of the Judges Cycle, so if you want to read what I think about that, go look at my Introduction to Judges. I guess the most significant thing stated here that I didn't mention is how the Judges Cycle reflects changes in the living generation. The generations that see the deliverance of the LORD are usually faithful, but when they die and a new generation emerges, that generation is usually faithless and seeks other gods. What I personally read from this is the importance of having a personal experience with God. If you are part of a people or generation that has seen the deliverance of the LORD, you will be faithful (excepting a few golden calfs - Ex 32). The future generations can see all of your memorials, observe your Passovers, see the stones that were taken out of the Jordan riverbed, or even sing the song of Moses (Ex 15), but when Joshua and the elders die, many people will find out that they never really had faith in the LORD, they were living in the shadow of somebody else's faith.
I do not say this to criticize the Israelites, but rather to allow their lives and stories to instruct us in how we should pursue the LORD. Living in the faith of another person can guide us well for a time, and it can serve as a model for us to follow, but there is an inevitable day when everyone must either stand in their own faith or they will fall. That is the testing that the LORD speaks of in v. 22.
Memorials of past victories are good, but they are not enough. Traditions and festivals of remembrance are good, and they can teach us, but they are not enough. The ceremonies of the law were not sufficient to keep the hearts of Israel pure and true when they were put to the test. That is, I think, one of the big themes in the OT and it shows very clearly in Judges and indeed, in this very chapter. Israel has had many righteous men and women, and many righteous leaders. But as verse 19 so grimly puts it, when the righteous leader dies, the sins that long laid dormant in the hearts of men come back to the surface stronger than ever.
In this way, the OT reflects an awful lot of hopelessness. There are times when the people turn back to god, but those times of revival are so often followed by an even greater darkness. What I believe, and what most Christians believe, is that these stories in the OT like the book of Judges is meant to show us the hopelessness of men who pursue righteousness by the law of Moses and by the covenant of Israel with God in Ex 19-24 laid out in that law. I have yet to reach the content of the NT, but it's important to know that the Christian bible is built around this duality: the failure of the old covenant to bring men into righteousness and the hope and resurrection (both literally and metaphorically) that is presented in the NT. I promise I'll talk about this a LOT later, but I think it would be instructive for my readers to begin viewing the OT in this perspective.