Clearly the central theme of the book of Joshua is the truth that God is a promise-keeper. Well over five hundred years before these recorded events God pledged to Abraham that ‘to your offspring I will give this land'. The land he is referring to is Canaan. From that time onward to the period of the conquest God repeatedly makes the same promise to his people. This promise occurs so frequently in the Pentateuch that it seems to be the theme sentence of the literature.
The writer of the book of Joshua recognizes the importance of this theme. The fulfillment of God's promises of a land are central to the book. He begins the book with it and brings to closure Joshua's final charge to Israel's leaders with it. And the promises of God as fulfilled are found throughout the book.
The truth that God fulfills his promise of a land for Israel also has great implications for the believer today, and that is one of the great applications of the book of Joshua. Those who are truly of God's people, that is, those who have been redeemed by the blood of Christ, shall inherit a land. However, that land is not the dry and dusty land in the Middle East today. Rather, the Apostle Peter tells us that God ‘has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead, to an inheritance that is imperishable, undefiled, and unfading, kept in heaven for you'. We as believers have God's promise of an eternal inheritance and the possession of an eternal land that is real, earthy, and substantial. And, like Israel, we will indeed receive our inheritance because God is a promise-keeper!