“Then Joshua commanded the officers of the people. ‘Pass through the camp. Command the people, ‘Prepare your provisions. In three days you are to cross over this Jordan, to go in to take possession of the land that Yahweh your God gives you to possess.’”
It is time to get ready, to move out to take the Promised Land on the other side of the Jordan River. You have 3 days to get ready.
“To the Reubenites, the Gadites, and the half-tribe of Manasseh Joshua said. ‘Remember the word that Moses the servant of Yahweh commanded you. ‘Yahweh your God is providing you a place of rest. He will give you this land.’ Your wives, your little ones, and your livestock shall remain in the land that Moses gave you beyond the Jordan. But all the warriors among you shall cross over armed before your kindred. You shall help them, until Yahweh gives rest to your kindred as well as to you. That is when they too will take possession of the land that Yahweh your God is giving them. Then you shall return to your own land. You shall take possession of it, the land that Moses the servant of Yahweh gave you beyond the Jordan to the east.’”
This is an obvious reference to Numbers, chapter 32. The Reubenites, the Gadites, and the half-tribe of Manasseh already have their land on the east side of the Jordan. However, they agreed to fight with their other tribe mates on the other side of the Jordan River. They are going to leave their families behind and then return to their east side land when the victory on the other side of the Jordan is complete.
“They answered Joshua. ‘All that you have commanded us we will do. Wherever you send us we will go. Just as we obeyed Moses in all things, so we will obey you. Only may Yahweh your God be with you, as he was with Moses! Whoever rebels against your orders and disobeys your words, whatever you command him, shall be put to death. Only be strong and courageous.’”
They will follow Joshua just as they followed Moses, no questions asked. If anyone disobeys or rebels against Joshua, they will be put to death. They add the Yahweh command of being strong and courageous in all that they do.