In this chapter, Joshua gives his final address to the leaders of Israel.
This is something of a tradition in the OT. Jacob for instance gave a grand old speech to his sons at the end of Genesis (Gen 49), and Moses also had a song and a long blessing for the sons of Israel before he died (Deut 32-33). Now that Joshua is dying, he also has to give his parting words to the people of Israel.
Jacob and Moses were a lot more mystical in their advice, giving long prophecies about the various tribes of Israel. Joshua, for his part, is a lot more practical, just reminding people to not sin. I'd say that Joshua's speech is actually very deuteronomic. In Deuteronomy, Moses frequently reminded the Israelites of the sort o dichotomy available to them, to either serve the LORD and live or serve idols and die (Deut 30:15-19 is the clearest example). Deuteronomy is centered around a "blessings and curses" mentality, that serving the LORD brings about some set of blessings, while serving other gods and forsaking the LORD brings about an opposite set of curses.
In this chapter, Joshua is essentially paraphrasing that language by saying that the LORD will help drive out the Canaanites if the Israelites follow him, but if they intermarry with the Canaanites and associate with them, then by implication the Israelites will also serve their gods (Deut 20:17-18), then just as the LORD has brought about the "good words" that he promised, he will also bring about the "bad words" that he promised if they were to stray from the covenant.
I guess that's it. This is a relatively short chapter, and it's made even shorter because Joshua is only repeating Moses here. I guess one thing that's a little interesting about this chapter is that it is the second time in the bible that the phrase "book of the law of Moses" is used, the first being in Joshua 8:31. We are literally in the first book after the Pentateuch, and people are already talking about the law of Moses. Deuteronomy calls it the "book of the law", but now that Moses is gone people have already named it after him. Anyway, it's not a big deal, so I'm going to move on to the next chapter.