For emphasis, God told Joshua three times that he would need to be strong and courageous in order to be successful against the Canaanites. There were a lot more Canaanites than Israelites at the time.
The people also needed to obey all the instructions Moses had given them so they could:
settle the land,
establish farms with successful production, and
build homes, villages, and cities.
The land belongs to God, as does the whole earth (Psalm 24:1). God brought Israel into Canaan as tenants, not as owners (Leviticus 25:23).