Joshua 1, Be Strong and Courageous!

Moses has died and the nation of Israel is now camped east of the Jordan, ready to go west into Canaan.

Joshua 1: 1-4, Go possess the land

After the death of Moses the servant of the LORD, the LORD said to Joshua son of Nun, Moses' aide: "Moses my servant is dead. Now then, you and all these people, get ready to cross the Jordan River into the land I am about to give to them--to the Israelites. I will give you every place where you set your foot, as I promised Moses. Your territory will extend from the desert to Lebanon, and from the great river, the Euphrates--all the Hittite country--to the Great Sea on the west.

Joshua, the "aide" of Moses (mentioned previously in Exodus) is given instructions to finally enter the land.  The Israelites are promised a large swath of land, from the Euphrates to the Mediterranean, land promised to Abraham's descendants in Genesis 17.  (This passage repeats the promise from Deuteronomy 11: 24. Today the region described includes parts of Iraq, Jordan, Syria, Lebanon and modern Israel.) 
The Septuagint (see here) renders Joshua's name as Ἰησοῦς, that is, Yeshua, the name of the future Messiah.

Joshua 1: 5-8, Be strong and very courageous!

No one will be able to stand up against you all the days of your life. As I was with Moses, so I will be with you; I will never leave you nor forsake you.

    

"Be strong and courageous, because you will lead these people to inherit the land I swore to their forefathers to give them. Be strong and very courageous. Be careful to obey all the law my servant Moses gave you; do not turn from it to the right or to the left, that you may be successful wherever you go. 

Do not let this Book of the Law depart from your mouth; meditate on it day and night, so that you may be careful to do everything written in it. Then you will be prosperous and successful.

Twice these instructions include the command to "be courageous".  Courage includes obedience to "this Book of the Law".  The Book of the Law is presumably the Torah (five previous books of the Bible) or at least the instructions given to Moses throughout the Torah.  The creation of this great nation depends on its faithfulness to YHWH as demonstrated in its obedience to the Torah. 

Joshua and the people are instructed to meditate on the Law daily. After reading some of the details of the Law in Leviticus, it is clear that in order to follow the regulations and sacrifices, one has to keep reviewing them and thinking about their implications.

Joshua is taking over the mantle of Moses. We will see, throughout this book, clear parallels between the calling of Moses and the calling of Joshua.

Joshua 1: 9,  Be courageous, not terrified!

"Have I not commanded you? Be strong and courageous. Do not be terrified; do not be discouraged, for the LORD your God will be with you wherever you go."

This is the theme of the book.  For a third time we hear, "Be strong and courageous." As before, the command includes a promise, "YHWH will be with you wherever you go."

Joshua 1: 10-15, Orders to the people

So Joshua ordered the officers of the people: Go through the camp and tell the people, `Get your supplies ready. Three days from now you will cross the Jordan here to go in and take possession of the land the LORD your God is giving you for your own.'"

    

But to the Reubenites, the Gadites and the half-tribe of Manasseh, Joshua said, "Remember the command that Moses the servant of the LORD gave you: `The LORD your God is giving you rest and has granted you this land.' Your wives, your children and your livestock may stay in the land that Moses gave you east of the Jordan, but all your fighting men, fully armed, must cross over ahead of your brothers. You are to help your brothers until the LORD gives them rest, as he has done for you, and until they too have taken possession of the land that the LORD your God is giving them. After that, you may go back and occupy your own land, which Moses the servant of the LORD gave you east of the Jordan toward the sunrise."

Joshua gathers the people and they prepare for battle. (The "officers" are most likely tribal elders, says Robert L. Hubbard.)  

The tribes of Reuben, Gad, and half the tribe of Manasseh, already possessing the east bank of the Jordan, are reminded that they too are committed to helping conquer the lands west of the Jordan. The people of Israel are to act as one united nation.

Joshua 1: 16-18, The people say, "Yes!"

Then they answered Joshua, "Whatever you have commanded us we will do, and wherever you send us we will go. Just as we fully obeyed Moses, so we will obey you. Only may the LORD your God be with you as he was with Moses.

    

Whoever rebels against your word and does not obey your words, whatever you may command them, will be put to death. Only be strong and courageous!"

The people enthusiastically confirm that Joshua is replacing Moses and promise to follow Joshua just as they followed Moses. The people acknowledge that treason in this endeavor is to be met by death.

Once again, for the fourth time in the chapter, we hear the rallying cry, "Be strong and courageous!"

This enthusiastic, positive response is relatively easy; it is the future action that will be challenging!  How this response plays out will be the story of the book of Joshua.