Joshua 1:8-9 Study this Book of Instruction continually. Meditate on it day and night and you be sure to obey everything in it. Only then will you prosper and succeed in all you do. This is my command--be strong and courageous! Do not be afraid or discouraged. For the Lord your God is with you wherever you go."
Just before this in Deuteronomy 34:9 the Bible tells us, "Now Joshua son of Nun was full of the spirit of wisdom, for Moses and laid his hands on him." Joshua was full of wisdom yet God told him to study the Bible as it was written so far. He was to meditate on it day and night. His wisdom, mighty as it was, still needed to be supplemented by God's word!!! We are never so smart that we don't need to keep reading and studying what God has to tell us. His word will keep us strong.
It is no wonder that in countries where they want their people powerless that they take away their Bibles!! That act in itself tells us how powerful God's word is.
Joshua walked with Moses, Joshua say God's miracles first hand, Joshua was given the spirit or wisdom...yet Joshua still needed to read and know God's word!! I think we do too!