Book of Joshua
With the death of Moses, Joshua takes over as the leader of Israel. He has been a helper to Moses from the time he was a young man and Israel came out of Egypt (Exod. 24:13; 33:11; Numbers 11:28). He was first mentioned in Exodus 17:9 when he followed the instructions of Moses and waged war on Amalek. His name was Hoshea (Oshea KJV) but Moses changed it to Joshua (Num. 13:8,16 [Jehoshua KJV]). This is a combination of the name of God (YHWH) and the Hebrew word for salvation and thus means 'YHWH Saves'. His name will appear in the various forms of Hoshea, Oshea, Jehoshua, Jeshua, and Jesus.
His job was to lead Israel into the land promised unto Abraham. The book is then a record of how Israel conquered the land. It appears that conquering the land took about seven years. We can note that Caleb was 40 when the spies were sent out. Caleb was 85 years old when the conquest was completed (Josh. 14:7-10). When we subtract the 38 years of Israel's wandering we arrive at the seven year figure.
Later we learn that Joshua was 110 when he died ( Josh 24:29). It has been guessed that there were about 13 -15 years between the events of chapter 14 and his death. Then the elders that knew him finished out their lives - another 7 to 10 years. We don't have anything exact to pin all this on other than the statement of Caleb. So it looks like we will pack about 20+ years of history into this book.
Reading allows us to look back and see what they were experiencing in real time. We see that God was working with them, protecting them, giving them the victories. They had to trust God. When they trusted him and did what He said, He caused them to overcome their enemies. When they rebelled against Him, he allowed them to lose the battles.
In preparing Joshua for this task, God admonishes him in several points.
First, be strong and of good courage. The admonition to "be strong and courageous" will be repeated throughout the book - look for it. Such strength and fortitude come from a complete confidence in God. The battle belongs to the Lord. Joshua had seen the power of God as he served as a helper to Moses.
Next, be careful to do according to all the law. This had been repeated many times throughout the book of Deuteronomy. It never is out of date! Joshua is to be full of care about following the law of God. He is to be careful to do ALL of the law. Walking with God does not allow one to pick and choose which commands of God he likes.
Then, do NOT turn to the right or left from the law. This obviously means not to deviate from what God has said. It doesn't matter which way we error from God's word, such deviation is wrong. Be careful NOT to go your own way but trust in the Lord.
In order to assure himself that he would not deviate from God's law, God admonishes him to "not let the word depart from your mouth - but meditate on it day and night." Memorize it, think about it, talk about it, teach it, and do it. This has always been the recipe for walking with God.
THUS, God assures him that THEN you will have good success. Joshua walked with God. Hence we read at the end of the book that he challenges Israel: Choose you this day whom you will serve" (Josh. 24:15). Serving God is always a matter of choice. What will you choose?