Joshua 23
God, not Israel, has conquered Canaan
The promised land includes everything between the Jordan and Mediterranean
Be strong (or rigid) in obeying everything in the book of Mosaic Law
Do not associate with, especially by intermarriage, the Canaanites
Do not serve any Canaanite gods
If you do associate with the Canaanites, they will destroy you
Most of the chapter is straightforward. However, we do get a small insight into the slow evolution of Israeli civic society from the structure of Exodus. Following Joshua, there is no single great leader. Instead, elders (zaqen), judges (shaphat), officials (shoter), and leaders (ro'sh) control the tribes.
Zaqen seems to have no implication other than persons of great age. Ro'sh ties back to Exodus 18:25, in which Moses at the suggestion of his father-in-law, chooses chiefs. Shaphat is the function of judging described for leaders in Ex. 18:26.
The elders (zaqen) were the cloud of witnesses at Mount Sinai who saw God (Ex. 24:9). Elders are not mentioned in Exodus 18 in the context of leadership. But the only officials (shoter) mentioned in Exodus are Egyptian overseers. The word used in Exodus 18 is sar, a generic word which applies to higher levels as well. Interestingly, Hebrew officials (shoter) are mentioned in Deuteronomy, and appear there to be somewhat inferior to captains of 10.
Another interesting point is that that the existence of an oral law of divine origin (Talmud) is inferred because Joshua orally addresses the leadership of Israel. However, it is persuasively argued that this is incorrect, that the oldest branch of the Talmud, the Mishna, emerged at the time of the Babylonian captivity much later (http://www.seedofabraham.net/talmud.html).