Chapter 1

2024 - 4 From the wilderness and this Lebanon as far as the great river, the river Euphrates, all the land of the Hittites to the Great Sea toward the going down of the sun shall be your territory. [Jos 1:4 ESV], much like the passage in Deuteronomy.

Compared to here:

24 Every place on which the sole of your foot treads shall be yours. Your territory shall be from the wilderness to the Lebanon and from the River, the river Euphrates, to the western sea. [Deu 11:24 ESV].

That second one says from the Euphrates to the Med flat out.  Joshua was sitting on the banks of the Jordan when God said this.  So the Joshua quote says from the Jordan to the Euphrates to the east, and from the Jordan to the Med to the west. 

But Israel has never in their history possessed all this territory.  What they did possess is the land that Moses saw from Mt. Nebo, described this way:

1 ...Gilead as far as Dan, 2 all Naphtali, the land of Ephraim and Manasseh, all the land of Judah as far as the western sea, 3 the Negeb, and the Plain, that is, the Valley of Jericho the city of palm trees, as far as Zoar. [Deu 34:1-3 ESV].

What Moses saw is what they actually did conquer.  What Moses saw is how far they got before they began to stray from God so badly that he would no longer help them. 

God tells Joshua what is to come.  Joshua is to lead the people in the conquest of Canaan, the fulfilling of God's promises to Abraham through them.  But there is a requirement.  This command:

7 Only be strong and very courageous, being careful to do according to all the law that Moses my servant commanded you. Do not turn from it to the right hand or to the left, that you may have good success wherever you go. [Jos 1:7 ESV]

The Law was part and parcel to what was to come.  It was not temporary, and it was not to be discarded once they were successful.  All was conditional on keeping the law, and doing so with care and attention to detail.

These first verses are sort of God's commission, given to Joshua.  In that commission is the following:

8 This Book of the Law shall not depart from your mouth, but you shall meditate on it day and night, so that you may be careful to do according to all that is written in it. For then you will make your way prosperous, and then you will have good success. [Jos 1:8 ESV]

Joshua gives three days notice for the people to prepare to enter Canaan.  The time has come.  It must have been quite exciting.  He reminds Reuben, Gad, and Manasseh of the promise they made to Moses, to go and help their brothers fight against Canaan, even though the land they want has already been taken.  They promise to follow Joshua in whatever he commands them to do.