The book of Joshua is a reminder of God's faithfulness and his call for us to be faithful to him.
At the start of the book of Joshua, Joshua is appointed as Israel's new leader, a new Moses. He commands obedience to the covenant, sends spies into the land, and brings the people of Israel through the waters of the Jordan River. There Joshua runs into a heavenly commander who makes it clear that the battles that will unfold in this book are not about Israel versus other nations but about God fulfilling his promise to the family of Abraham.
In the battles that follow, Israel learns the hard way to walk in covenant faithfulness. As they do, some of the Canaanites surrender, while most try to extinguish the Israelites. The justice that God brings on human evil finds unique expression in Joshua as God drives out the Canaanites. Having defeated their enemies, the people of Israel divide the land by tribe and receive final words of challenge from Joshua to remain faithful to the covenant.