Joshua 1:9 Have not I commanded thee? Be strong and of a good courage; be not afraid, neither be thou dismayed: for the LORD thy God is with thee whithersoever thou goest.
To be strong and of good courage refers to believing God. The simple thing is to allow your fear to get you off target. You listen to your doubts and fears. You listen to all that Satan would throw your way. He tells you that God is not with you, that the task is too big. He tells you that you will not be able to do what God has said that you can.
So it takes strength and courage to keep centered on the truth. This is not physical strength but spiritual! It is about believing and controlling your thoughts. It is about bringing all of your thoughts into captivity so that they will honor God!
God is with us. That is a fact. We must believe even when it is hard. Be strong!