The simplest and yet an important analysis of Joshua's literary structure is to note that the book is a bifid, a literary composition structured purposely as two halves. Other OT books with this structure are Isaiah, Ezekiel, Daniel, and Zechariah.
The first half of Joshua relates major events of the Conquest, those battles that denied to surviving Canaanites any possibility of preventing Israel from entering the land and beginning to settle it. Here the emphasis is on God's action on behalf of Israel that enabled them to possess the land.
The second half of the book centers around the allotment of the land among the tribes, with a view to their beginning settlement. Thus it has an aura of expectancy. This is heightened by the way in which the book is concluded, with Joshua's final words of warning and encouragement and his leading the people in renewing the covenant at Shechem.
There are also other more complex structural features of the book that mark it as a deliberate creation with purpose. For example, there are a number of “frames,” the most important of which frames the entire book. Ch. 1 records God's and then the people's exhorting of Joshua as he was commissioned to lead them into the land. Chs. 23 and 24 record Joshua's exhortations to the leaders and then to all the people as his death approached. Thus both the beginning and the conclusion of the book highlight God's faithfulness and the necessity of faithfulness on the part of God's people.
The allotment of the land also has a frame. It begins with the apportioning of Caleb's inheritance (14:6-15) and ends with the apportioning of Joshua's (19:49-51).
The major theme of Joshua is the recounting of God's actions in fulfilling the promise to the patriarchs: this land would be the inheritance of their descendants, though they themselves were dwelling in it as sojourners. God's opening charge to Joshua in ch. 1 and the notice in 24:31 that the elders with Joshua had known all the work Yahweh had done for Israel make it clear that the initiative was God's and not Joshua's.
Other themes of the book are the need for holiness on the part of God's people, the reality of judgment upon sin, the land as part of the spiritual inheritance God gives his people, and the importance of passing on the memory of God's actions in the past as a means to faith for the future. This last theme may be described as the author's purpose in writing the book.