In Joshua 1 God is talking to Joshua and telling him what is going to happen from here on out. God is really telling him much more than He tells most people. "No one will be able to stand before you", "I will give you this land from here all the way to here", "Be strong and courageous and follow my Law and I will give you success".
There are a lot of promises in these 1st 9 verses and God doesn't tell Joshua to do too much. God is the One working, not Joshua. Joshua has to be strong and courageous and to follow the Law that God gave to Moses and that is it.
Why strong and courageous? God knew that Joshua was going to be tempted to be afraid. God knew the people He would deliver into their hands were mighty compared to Joshua, but not compared to Him. Joshua would be tempted to look on the outward appearance of his enemies, but God was way bigger than they were.
God also knew that it would be very tempting for Joshua to not stick to the Law, but to turn away from these commandments. No other nation would be doing the things that they were told to do. Not other nation would be sacrificing so much of their livestock to atone for their sin. No one else had to keep the Sabbath holy. It would be easy to start to fall into the practices of other nations and God knew that would be difficult for them to do.
He keeps giving Joshua the same commands because He wants to make sure that Joshua gets it. Kind of like when we tell our kids, "Be home at 8. What time are you going to be home? Do your friends know that you have to be home at 8? What time was that again?" It was important for Joshua to get it so he could pass it on to those he was leading.
The commands are limited and the promise is huge. Do this and "I will make your way prosperous and you will have success". All the work is on God's part. He will be with them, He will deliver, and He give success. What a comfort that had to have been. All Joshua had to do was be strong and courageous and follow the directions God had given and God would take care of the rest.
Isn't the same promise true for us today? Do we not just have to trust and obey and He will take care of the rest? Even though the things around us seem large, can't we just see that God is so much bigger than they are? Don't we just need to stick to the Word, hide it in our hearts, and let God take us where He wants?
It is certainly not rocket science, and that may be our problem. We try to make it more difficult. Trust God and obey Him. He has the rest covered.