While not the only theme of the book of Joshua, a strong current within the text is a handbook, if you will, regarding the qualities necessary in righteous leadership. Joshua is not the first significant leader of the Old Testament; he follows Abraham, Noah, Jacob, Moses, and Aaron. However, his lot is given to him from the former leadership of Moses — the one who lead the people of God out from the hands of Pharoah. He came to leadership having apprenticed under Moses and learned the habits of leadership, and consequences of failure, vicariously through Moses.
God establishes a relationship with Joshua that is grounded in Joshua having a personal experience witnessing God’s hand on His follower Moses: “Only be strong and very courageous, being careful to act in accordance with all the law that my servant Moses commanded you; do not turn from it to the right hand or to the left, so that you may be successful where your go” (Joshua 1:7). God restates this encouraging message a few verses later. Joshua, in turn, spoke to his leadership regarding what God expected of them as a nation. It is through their response to Joshua that we can see his effectiveness as a leader: “Whoever rebels against your orders and disobeys your words, whatever you command, shall be put to death” (1:18). They echo the words of God and encourage their leader in the final verse of chapter 1, “Only be strong and courageous.”