Only be strong and very courageous, that you may observe to do acording to all the law which Moses my servant cammanded you; do not turn from it to the right hand or to the left, that you may prosper wherever you go. Joshua 1:7
God never, ever tells you do to something that is completely impossible to do. Now, it may be impossible for you to do in your own strength, but with God all things are possible, especailly the things that He commands you to do. This verse commands us to be strong and courageous. Therefore we can know that strength and courage can be and should be ours.
God commands Joshua to be strong and courageous that he may, “observe to do according to all the law.” Sometimes we disobey God’s word out of fear. Fear of what others think about us, fear of what could happen to our reputation, fear of failing God, fear of failing ourselves, fear of not being able to finish what you start, and so on. We need courage to overcome those fears. God commands us to have that courage. The good news is that God has given us that courage and strength in Christ:
For God has not given us a spirit of fear (or lack of courage, you could say), but of power and of love and of a sound mind. 2 Tim 1:7
Thank God! In Christ we have couarge, power, love, and soundness of mind (or self-discipline as some translations say).
Notice how I say “in Christ” to qualify my statements. All these things, and everything in the christian’s life, only work when you are remaining in Christ; that is, abiding in Him and allowing His word to continually abide in you according to John 15. Nothing will work for you if you are living in the flesh or trying to do anything in your own strength.
So the point is, when you remain in Christ, you can live with strength and couarge to face anything that may come your way.